Yes, I understood perfectly.
I find myself with the same problem.
I created this tool for myself many years ago, every time a plugin is updated new ones appear and old keys disappear, and no plugin warns that the language file has been modified. Also, most plugins do not remove the keys of a plugin when it is uninstalled. So I fixed the presentation, I put an installer and an uninstaller and put it on sale.
It does everything, except the translation itself. For example, for the keys of the plugins management panels you can leave the original content in English and only translate the front-end users, with that you save hundreds of "copy-paste"
It is completely free of errors, explanatory tooltips on all the buttons ... But no, it has no interface with the Google translate API because it is for payment.
There is a lot of information on the Internet about how to cheat and not pay for this, for example:
https://ctrlq.org/code/19909-google-translate-api
but they are illegal and can not be included in a commercial plugin.
Behind Language Manager there are many hours of work, watching other 10USD plugins I think it is very cheap, very useful and with very good technical support. Seeing how little has been sold I do not think it would sell anymore because it adds more benefits