Language switcher for theme

Hello,
I translated my theme into another language using the Loco Translate plugin. Unfortunately, the plugin does not offer a language switcher. What are my options for implementing a language switcher?

PS: Theme is the only thing I want to translate. I’m not going to create a multilingual web network (so I won’t translate pages or posts).

If something like this is impossible, I would at least need to ensure that the website is always displayed in another language (Czech), while the administration interface remains the same.

thank you for answer

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