Forgive me for writing in this section, but unfortunately the Russian section does not exist here.
Also, please forgive my English.
As early as 2 years there has been a problem with the Russian translation for K2.
There are extra _QQ_ characters in the localization file that replace quotation marks, and some lines (especially the administrative part of the translation) are commented out.
In addition, it seems that lines from files are deleted, since translations of earlier versions were more extensive.
I have a more or less adequate translation, this is partly your old translation, but it has been supplemented by me.
I ask you to replace it, we have been discussing this problem for a long time in Russian-speaking forums dedicated to joomla (at least with the release of release 2.7.1) for example joomlaforum(point)ru/index(point)php/topic,345159(point)0(point)html

The version of translation I have attached, although not complete, but by correcting your version, I realized that I have it much better. I attach it in the application. Thank!

The problem exists, but as it turned out, the essence of the problem is not in the translation, but in transifex, from which this translation comes.
In short, I read the announcement at www.transifex.com/joomlaworks/k2/announcements/10564/ and note that the problem is probably due to one error:
"The problem is that some language packs, especially the oldest ones and as such the most popular ones, continued to use the "_QQ_" identifier as a way to insert double quotes in translated strings. This identifier was removed in recent Joomla versions (possibly at around mid v3.8.x) and as such "breaks" any language file that still references it."
As you can see from the variable PLG_GMAIL_XML_DESCRIPTION, which is located in the file /administrator/language/en-GB/en-GB.plg_authentication_gmail.sys.ini Joomla uses "_QQ_" to insert double quotes.
All "_QQ_" on transifex has been replaced by \", however, at the output, transifex changes them to \\"_QQ_".
In this way:
\" becomes \\"_QQ_";
" becomes "_QQ_ ";
Checking this is very easy, just on the translation page on your website you need to download the English language and install it on top of the existing one (which is put together with the component itself, due to which, apparently, no one noticed this bug), and then find it when you switch to the component K2, that instead of English, you display the variable keys.

It turns out that you do not need to escape quotes, but then a new question arises related to the use of a single quote ('):
It can be used, but not everywhere.
So, for example, if you look at the Japanese localization of the component, you will notice that they decided to use this particular method, but when using it in the backend, an error occurs when trying to exit the K2 component parameters item, which is (probably) related to the presence of K2_THE_ENTRY_IS_ALREADY_IN_THE_LIST
and
K2_THE_ENTRY_WAS_ADDED_IN_THE_LIST
in javascript.

In connection with the foregoing, I believe that it would be correct:
 1) Correct English localization on transifex, that is, if possible, get rid of quotes escaping. That is, instead of (\") use (").
 2) Issue an announcement about this, since I suspect that the Japanese are not the only ones who decided to use single quotes.
 3) There is no K2_PARAMETERS variable on transifex you need to either add it or, in my opinion, it is better to replace it with one of the global joomla variables JGLOBAL_FIELDSET_BASIC or JOPTIONS.
 4) I, in turn, will be engaged in Russian localization, I think that putting it in order will not take much time.

I apologize if all this seemed critical to you, I just think that many other countries may also have problems with translation or functionality - as happened with the Japanese translation. My concern is caused only by the fact that I myself often use your component and I, like many other users using K2, would like to see the development of this project.

Sorry for English again. I speak only German and Russian, and probably how Google translates my words translates looks just awful.
And yet ... I would be very grateful if you could have opened a topic for the Russian community on the forum. I managed to study your component quite significantly and maybe I can answer some questions of users from Russia myself.
I can’t guarantee that I will do this every day, but once every 3 days it’s quite realistic for me to check for new questions in the thread. Thank you for attention.

I sent you a message at www.transifex.com
I think the question can be partially closed.