If the comment line contains the name of the theme/plugin/author/website address than it should not be translated.
Currently the name is translated

Some examples with new version, blank behind is not removed.
Houd er rekening mee dat de huidige %s -module is verouderd en zal worden verwijderd in toekomstige updates. Gebruik in plaats daarvan de module %s .

Here the blank is removed, which in this case is wrong
Ga na het instellen van het aantal naar%s om elke gateway-optie in te stellen.
It should be
Ga na het instellen van het aantal naar %s om elke gateway-optie in te stellen.

Products %from% - %to% from %total%. Products on page %select_form%
Blank not removed behind
Producten % van% -% tot% van % total% . Producten op pagina%select_form%Here the last % is missing original :Use %s variable for product's base price. For example: %s.
Gebruik de variabele %s voor de basisprijs van het product. Bijvoorbeeld:

Here it is removed where it should not be removed
Hello %1$s (not %1$s? Log out)
Hallo%1$s (niet%1$s? Uitloggen )

If a translation from Google does not start with a capital, but the original does start with a capital, it would be great if that is corrected on the fly. Also if the line should start with a blank, Google removes that, so that should be checked as well. Same for '' which Google sometimes does not translate.

After the placeholders are in place and sent to Google, within the answer they are on the wrong place
Original line
By checking this box, I agree to the WP EasyCart %sterms and privacy policy%s
Translated line
Door dit vakje aan te vinken, ga ik akkoord met de voorwaarden en het privacybeleid van WP EasyCart %s%s
Line before sent to Google
processPlaceholderSpaces found it in original: By checking this box, I agree to the WP EasyCart [0]terms and privacy policy[1]
Link to translation
https://translate.wordpress.org/projects/wp-plugins/wp-easycart/stable/nl/default/?filters%5Boriginal_id%5D=11197957

If you add a replacement verb, and you hit enter a new line is created
But this newline is not handled properly, because it generates this error
undefinedHundefinedeundefinedtundefined

If a sentence contains a quote around a placeholder, some strange behavior is present after the translation
Original
Booster: Free plugin's version is limited to only one "%1$s" product with settings on per product basis enabled at a time. You will need to get Booster Plus to add unlimited number of "%1$s" products.
Translated
Booster: de versie van de gratis plugin is beperkt tot slechts één ";%1$s"; -product waarbij de instellingen per product tegelijk zijn ingeschakeld. Je hebt Booster Plus nodig om een onbeperkt aantal ";%1$s"; producten toe te voegen.
link to line
https://translate.wordpress.org/projects/wp-plugins/woocommerce-jetpack/stable/nl/default/?filters%5Boriginal_id%5D=4801170
It can be fixed by adding this into the verb replacement ->"," e.g. replace '"" by the quote '"' sign

If a original line contains a html replacement like ’ which is the replacement for "'", it is not removed after the translation
Example
It seems we can’t find what you’re looking for. Perhaps searching can help.
Het lijkt erop dat we ’ niet kunnen vinden wat u ’ zoekt. Misschien kan zoeken helpen.
If it is put in the replacement list, then an error is thrown.

This could be prevented when the API key is checked when saving the settings.

in the current version a warning is shown when a glossary word is not present within the translation.
That is a great functionality, but it would save time if you could also define a list of verbs that automatically are replaced.
Because not all lines in the glossary can be used for that purpose depending on the translation
But there are some verbs/nouns that can be replaced independent of the translation
Example in the nl_NL glossary we have "website" which should be translated as "site"
This is a verb that is very often used, so instead of the warning it can be replaced automatically
This would again save time

If a translation contains the following placeholders > and &, then the will also get a blank behind the & character
So &g;t becomes & gt; and &amp becomes & amp;

Google messes up the placeholders by adding spaces. To convert it back to the original the spaces need to be removed. This has partially been fixed, but in the following situation it does not work
Original line contains:
an %1$soutdated
Translated into locale nl_NL:
een% 1 $ verouderde

The blanks are not removed, and the "s" character is missing
Test line in wordpress.org
https://translate.wordpress.org/projects/wp-plugins/all-in-one-seo-pack/dev/nl/default/?filters%5Boriginal_id%5D=10991311

With the latest version you have the option to store translation improvements after the add-on retrieves translation.
As long as you keep the add-on active, they stay in memory.
But if you disable and enable the add-on, they are gone.
That is not very friendly, because sometimes you need to disable an add-on for troubleshooting purposes.
It would be better to store them in the same place as the API key and glossary file.
Especially if you have a large list of substitutions.

If you change some verbs in the options, but do not select a glossary file, then this option will return an empty value
When saving options without selecting a file, the previous value if it contained one should be taken

If a verb in the glossary has lowercase it is considered wrong if the translation has a uppercase
Example glossary has template, template
Translation has Template, it is considered an error
If you add the same verb into the glossary, then the match does not work
If you alter the Uppercase into lowercase, then the bar becomes green
Maybe consider to alter the behavior, so if a verb is present with lowercase, then the uppercase verb is also considered to be good
Test link below
https://translate.wordpress.org/projects/wp-plugins/ecommerce-product-catalog/stable/nl/default/?filters%5Bstatus%5D=either&filters%5Boriginal_id%5D=1538147&filters%5Btranslation_id%5D=76357103

If you translate manually without the button "Translate" it will show a colored bar if there is a word not properly translated as is in the glossary. If you save such a translation and reopen the translation, I would expect the colored bar to popup again, as the translation contains a word that is not ok according the glossary

Here the word "pagina's" is the same as within the glossary, so either a green bar should be shown, or the colored bar indicating the error as it previously stated "pagina's"

In case a line contains the following original
The permalink for the current page/post.
De permalink voor de huidige pagina / post.

The forward slash gets a blank before and after
So if possible they should be removed

That also happens with the "&" in some cases, but will be hard to fix
The permalink for the current Proctor&Gamble.
De permalink voor de huidige Procter & Gamble.
It depends on the verbs present in the original
Because sometimes for the locale the & sign is replaced by a verb, so then the & is no longer present

This would need implementation of a new table containing those wrong placeholders, like the glossary table. Or maybe a regex function that could do that.

If you have a translation that includes a plural line, then only the single line is translated

When a sentence has a # it is not placed into a placeholder, and therefore gets a blank behind it
Original
%1$s (#%2$s)
Translated
%1$s (# %2$s)
Link
https://translate.wordpress.org/projects/wp-plugins/wc-frontend-manager/stable/nl/default/?filters%5Boriginal_id%5D=8962169
This can be resolved by putting it into the verbs replacement list

Currently if there is no translation, it will be fetched from Google, which costs money
There are a lot of default translations in every plugin/theme
So before demanding the translation from Google or other translation engines, a search in the local database could be done to find a default translation. Then it would not cost money and might be quicker to translate under circumstances.
Example "Save", "Next", "Previous", "Back" those are all default translations
Example "Are you sure?"
Example "Select a page"

If a translation includes a % before and after a verb, then there is no placeholder created
In this case there can be blanks after or before, when translation is applied
%product_title% is not available until %direct_date%.
% product_title% is niet beschikbaar tot %direct_date%.
Link to test item
https://translate.wordpress.org/projects/wp-plugins/woocommerce-jetpack/stable/nl/default/?filters%5Boriginal_id%5D=5659716

Sometimes depending on translation the translated line does not start with a capital
If the original does have a capital, then the translated text should also have a capital at the beginning
The other way around if the original does not start with a capital, then the translated line should also not start with capital

Google has the habit of adding blanks after html characters, which is very annoying
This example is happening always :Get started here.
It will be translated into : Ga hier aan de slag .
It is not that big a problem, but it will possibly marked as fuzzy if you do not notice it, because the it checks for html errors

The following placeholder stays behind after translation ’
Example:
It seems we can’t find what you’re looking for. Perhaps searching can help.
Het lijkt erop dat we ’ niet kunnen vinden wat u ’ zoekt. Misschien kan zoeken helpen.
Putting it into the replacement list without replacement would be a solution
But that does not work currently.
’,test
Result
undefinedHundefinedeundefinedtundefined

Currently it is possible to translate a single line (great function)
But we also have 100% suggestions if we go into the to translate line
After you go in you will see 100% suggestions below the empty box
I think it would be great if the first of those suggestions can be copied into the textfield automatically
If the 100% suggestion is fine than it saves translation via Google, and you do not need to click on copy below

If the extension translates, it gets the formal translation back. This is a bit annoying as the sentence is not correct. There are several locales that have a formal translation as well.
There is no official toggle to change this, however there is a solution obviously, as with deepl.com there is a toggle to change this
The solution is not that difficult, example below.
Sentence: You are a nice person
Translated: U bent een aardig persoon
Change the "You" into "Je" which is informal
Translation: Je bent een aardig persoon
Notice the change in the first two verbs
Germany has formal
Belgium has formal
This is obviously a new feature, but important to have. When implementing it should be possible to set the verb to trigger this as a param, or there must be an official toggle to switch it. When translating you need to set this in the project to switch to formal

Before adding the button within the translation line the bar changed from color if you corrected the translated line.
That does no longer change color, if red it stays red

If a glossary word contains a quote like this:

This is in the red line for the warning not shown properly because it shows the old method pagina's
That will cause people to use the old method, which is no longer necessary.
It is better to show the word which is present in the glossary e.g. pagina's

There is a problem with replacing the placeholders. Sometimes you get a double Font-size adjustment in more places: now, font-size controls are right where you need them in the List and Code blocks. No more trekking to another screen to make that single change!
Translated
Aanpassing van lettergrootte op meer plaatsen: nu zijn de besturingselementen voor lettergrootte precies daar waar u ze nodig hebt in de lijst- en codeblokken. U hoeft niet meer naar een ander scherm te trekken om die ene wijziging aan te brengen!
It depends on the length of the sentence in my opinion

Now with the verb replacement list in the options, it would be welcome to be able to export/import them
That saves a lot of work, especially if you have a large (glossary) list.

If a sentence contains the same placeholder more than once, the replace currently replaces all matching placeholders.
As we know the position of the placeholder, we need regex replace to replace only the position
Example line
%2$s published. %1$sView %2$s%3$s.
Translated with my latest version (my current version does not not remove the blank behind in this situation)
The line below is as a result of my default replace without regex
Now it goes wrong because it finds two times %2$s and this removes the blank after the first one as well
%2$sgepubliceerd. %1$sZien %2$s%3$s.

Tested with restopress development
https://translate.wordpress.org/projects/wp-plugins/restropress/dev/nl/default/?filters%5Boriginal_id%5D=8742207

For the reason of checking which glossary file you are using it would be great if the is shown above the select file button
Because if no file is present, the glossary check will fail
The only option you have now is to reload it

There are a lot of standard translation lines, that could be put into a database/file, which could be consulted before submitting a request to the API. If it finds the line within this file, then take that instead of making costs by requesting translations

Sometimes %d is not a placeholder, but it is a preceded by a % sign, so it should not be treated as a placeholder for %d
Test example:
https://translate.wordpress.org/projects/wp-plugins/woocommerce-jetpack/stable/nl/default/?filters%5Boriginal_id%5D=5659716
Original contains:
%product_title% is not available until %direct_date%.
Translation contains:
% product_title% is niet beschikbaar tot %d irect_date%.

If a line contains a placeholder embedded in quotes, the after translation the quotes are replaced by their html value
Original line
Continue reading "%s"
Translated
Lees verder "%s"
This might be solved if switching to send "html" instead of text.
It is partially a duplicate of other Google API related issues, but I think we need to separate them
https://translate.wordpress.org/projects/wp-themes/bizbuzz/nl/default/?filters%5Boriginal_id%5D=9902308

If a text contains "\n", than this is not handled, the "\n" is removed

Currently the UI is in English in FireFox and Chrome, for internationalization it would be great if the add-on would be in native language.
Low priority

It appears that %1s is not put into a placeholder, which causes a blank between % 1s
Link to test with
https://translate.wordpress.org/projects/wp-plugins/mainwp/stable/nl/default/?filters%5Bterm%5D=%251&filters%5Bterm_scope%5D=scope_any&filters%5Bstatus%5D=untranslated&filters%5Buser_login%5D=&filter=Apply+Filters&sort%5Bby%5D=translation_date_added&sort%5Bhow%5D=asc
Original text
No ignored %1s
Translated
Geen genegeerde% 1s
Debug dump
After pre-processing: No ignored %1s googleTranslate.js:313:13
format type text googleTranslate.js:53:13
request body
Object { q: "No ignored %1s", source: "en", target: "nl", format: "text" }
googleTranslate.js:61:13
sendAPIreQuest original_line: No ignored %1s googleTranslate.js:68:10
Translated text: Geen genegeerde% 1s

If a translation line is empty it gets RED flagged due to the fact that it is not finding the glossary verbs.
This seems a bit strange to check for glossary verbs if the line is empty.
I think it would be nicer to not check the glossary if the line is empty, just only check it if there is a translation present

If you go into a already translated line, and you select "translate" then nothing happens.
If you select the general "translate button" then the line gets translated.
So it appears that the translation function is not called if the translation is already present
For practical purposes this should also work in already translated lines using the inline button (test purposes originally)

Create a guide here in the WIKI section, for example. How to create that API key.