[taos]

1. There should be no en in ExtraLocales because its one of the included languages - if you change something in the conf file make sure to restart the Kobo in this case.
2. If - after a restart - you still see "Extra:_en" instead of "English" then something is wrong. Depending on how much you've already done to customize your reader you could either try a factory reset, update to the latest firmware, install the patched software, and then follow again the instructions to add additional dictionaries. Or:
3. Go back to the original it-en dictionary (copy it back, sync it, or download and sideload it).
4. Restart your Kobo. Have a look at the entries in the dictionary dropdown menu: if everything works as expected ("Extra:_ru - English" entry, when you choose it you're either told that it can't find the definition or you're shown it), great. If not:
5. Open the database, choose the dictionary table, remove the entry for the ru-en dictionary completely, save the database, disconnect your Kobo safely and restart it.
6. Can you now use one of the pre-installed dictionaries (especially it-en) again? Are the entries for English actually shown as "English" and not "Extra:_en"? If yes, edit the database to add the line for the new dictionary again, make sure to use exactly "-ru-en" without trailing spaces, make sure that the size is correct, restart your Kobo afterwards. If not:
7. Do a factoty reset and start all over.