How to translate images alt and description

Hi
I didn’t reproduce your issue with the 1.7.12 and the 1.8beta1.
For a French media, Polylang copies in its English translation the French Caption/Alternative text/Description.
Then if your modify them in the English media, they do not remove the Caption/Alternative text/Description in the French media.

I have Russian and English and Nivo LightBox. So, in media files(after update) when i switch language, translation stays, such as in nivo in adding images menu from media library. So it is possible to switch alts automatically, or i must to create 2 galleries in different languages?

Your issue is in the Media > Library or in Nivo Lightbox > All galleries?

So i resolve this issue. In the top(admin bar) there is switcher(all lang, eng, rus). Check rus->go to library, check image-> go to “change another details”. In opened page there is + near english. Push->translate->update. In lightbox in the top(admin bar) check eng->configure(adding images in nivo)-> add from library-> it shows only eng translated images. So in my gallery if it was 4 pictures in rus, now 8 – 4 rus, 4 eng…so very disappointing in this plugin. Many steps…i have more than 3000 photos…do you understand how much time i will spend? Very bad…very sad

In media library, when i select picture i want to complete rus alt text, then switch to english and complete translation without copiyng text in another language..

The “Show all languages” filter is explained in the Polylang documentation and it is set by default on “Show all languages”.
See: https://polylang.wordpress.com/documentation/setting-up-a-wordpress-multilingual-site-with-polylang/user-personalization/

Are you kidding me? When i switch (in the top) ALL languages, then if i check image(open the window, where i can input alt, descr and caption, ) i find rus text(mine), in this window under “user” there is switcher(not in top admin bar), and when i set eng and traslate, my rus text is GONE.