about localized upper/lower cases in common words

What project was that done for? Those changes to the English text should probably be reverted. It is Really Bad to Use Title Case for Things that Aren't Actual Titles, even in English. You should definitely follow the rules for your language.

I agree with you. My example comes from iNaturalist:Add observations project/fr so project is "iNaturalist:" and there is a bulk of such messages where nouns have been prettified. I started to keep messages as before in FR as long as only uppercase was concerned, and stopped to translate when posting this subject. I dont know if there is a filter and how the adequation "message to be translated" is evaluated but I realised we were losing energy with such cases. More of that I have thought about German language in which the upper case for common nouns is a rule: ... they will see no difference.

Yeah, that's basically just a stupid decision on their part, but I don't have any involvement in that project, so I don't want to try and change that, but just stick to the rules of your language. If your language doesn't normally do that (few languages do in my experience), don't use Those Annoying Capitals, it will just look silly (and possibly even unprofessional). If I see something written like that in Norwegian, I automatically think that it's autotranslated garbage, or that the person who wrote it barely even passed primary school, since they obviously don't know how to write Norwegian properly.

I agree, but as it's not a rule of english language, it's either a mistake of iNaturalist developers, or a particular will independantly of grammatical rules. So if we think it has no sense, the english messages must first be modified, and then the translations will follow. Otherwise, why this change in english only?