Is there a way to localize Pagespeed widget?
I must translate it by end or is there a way to specify the lang?
No, not that I am aware of. The strings come from Page Speed itself which is compiled into pagetest.dll. You might be able to specify a language at the time of the testing if you add support to it to pagetest.dll but that would be quite a bit of work (may be easier to just have a substitution on the server side for all of the known english strings).