I have just installed Xamarin Studio for the first time on Win 7 and I am using a localized language (not saying which one). Version 4.2.3 build 60. This should be the latest version as of writing.
What I found is that the translation is completely half-baked and not taken seriously at all by Xamarin, and if any QA and testing was made, it clearly did not catch these issues. First problem: the menu bar is localized, but the home page appears in English. On the "File" menu, "New" and "Open" is in English, "Save" is in English, but "Save As" is localized! "Page setup" is in English, but "Print" is localized. This goes on and on for every single menu, which is a mixup of two languages. It almost feels like an insult to my language. I could forgive if the documentation was localized with spelling errors, but not for the main menu bar and all essential options. If it is assumed that this is the kind of UI experience that the user is supposed to have, it is a truly sad state of affairs.
But this is not enough. I tried to switch the entire UI to English, through Environment > Language > User Interface Language. Set it to English and restarted, and it still appears with a mixup of localized terms and English. Apparently the setting did not have any effect.
What is the QA team doing?