Abbreviations of languages
I don't mind. I suggest just leaving it as it is now. There is no need to copy Wikipedia exactly.
This is not coping Wikipedia, I mentioned this encyclopaedia only as example. Just different lengths of abbreviations, as for me, are looking not very good. And it is a bit strange.
I agree with Bertran - we need to follow one set of language codes, ISO 639-1 probably being the best option. The language templates should be predictable - if a user sees that the French template is called "fr", then they should be able to correctly predict that the English template is called "en" and not "eng".
Also, if we eventually decide to set up a separate foreign language wiki, we'll use the same language codes for interlanguage links as Wikipedia (i.e. [[ru:Whatever]] etc.)
If standards exist, then follow them. I'm easy going on it and don't particularly mind but it would be best to do it now while there are only a few pages to change.
Done. Please, fill section "usage" in documentation of template:ru. I'm afraid that I can do it properly. Thank you.