Unit tests are probably not the best way to test software localization because there is typically a single function that retrieves the proper text from the application resource dictionary.
Typically, localization testing would be done with either UI automation or manually, and would be best handled with a combination of UI automation and manual testing. You would use UI automation to verify that the strings match the expected value for the chosen locale/language. Manual testing would check that the translated strings didn't overlap text, wrap inappropriately, or be cut off.
You'd also want to use manual testing to check input in the different languages. While you could automate some of this, the automation would not catch problems with keyboard input in the other languages - something I've experienced. A US-English keyboard configured to type Turkish gave the software no problems, but a Turkish keyboard caused errors with one specific input. Test automation can't catch this kind of thing.
In the localization testing I've done, there were two phases. Phase one was to check that all the strings used for menus, labels, and buttons were localized. To do this, the software had a fake language that rendered every localization as a random string of numbers. We'd switch to the fake language, then go to every screen looking for anything in English.
Phase two checked that the localizations were correct. For that, there was either someone who spoke the language in question or Google Translate. Again, we'd go to every screen, and check that the correct strings showed up for the language, and that the screen looked right. Since English is a very concise language when it needs to be, most of the localized strings are longer in other languages, which meant that buttons could end up overlapping each other or labels would wrap when they shouldn't, and so on (in my experience, German is the worst for word length, Spanish can be quite wordy, and languages that use different alphabets can cause issues with display sizing because something that's perfectly readable in English with an 8 point font size will be impossible in say Japanese with an 8 point font size).