In Thinking Sphinx, these settings are managed in a per-environment manner within config/thinking_sphinx.yml - similar to config/database.yml. The default settings should actually work fine with Cyrillic characters, but I think the issue here is that Thinking Sphinx now expects Sphinx v2.2.x by default (which uses UTF-8 automatically and has deprecated charset-type). To explicitly set that, add the following to your config/thinking_sphinx.yml file:
I would recommend using Sphinx 2.2.11 instead, though - and this is also managed in config/thinking_sphinx.yml:
Once you've made either of these changes, you'll want to run rake ts:rebuild to ensure the data is re-indexed accordingly.