I have chosen to write in 3 languages. I change them with the command Shift + Alt and it changes, but I cannot see in what language I write in the language indicator in my panel.
Can you help?
I'm guessing you are using ibus from the details you give.
To get your languages shown at the bottom, you need to change some settings.
Click on the language indicator and follow this video: Enabling Ibus Language Panel
(If you cannot see the video clearly: Click the ibus indicator, click preferences, and enable "Show Language Panel > When Active")
NB you might have to restart ibus after this. To do that click the icon and click restart in the menu