The auto-detected language in the Pop-up Bubble is not displayed due to the lack of space.
If you want to see the detected language, choose ANY language from the source language list.
The automatic language detection will be instantly performed, and the "detect language" will be switched to the DETECTED language.
Make sure that the "Detect source language automatically" checkbox is enabled in Pop-up Bubble Options.
If you want to keep this language for future translations, lock the source language by marking the checkbox next to the displayed language. This will temporarily disable the automatic language detection.
If you want to keep this language as a default language, go to Options and make desired changes.
This functionality is effective in the Pop-up Bubble Translator in all translation extensions: Chrome, Firefox, Opera, Yandex.