Pager labels aren't translated
I have seen this too. Looking thru the code, it appears that the pager templates do have translations set up properly. So in theory, UI translations should work. But they don't.

I haven't tried it but you probably could do this thru the hook_preprocess_pager__page(&amp;$variables) function (for full views pages).  There seems to be a $variables['pager']['#tags'] array with the values for pagers. You might be able to do the UI string translation here.