I disagree here. I actively use 4 different languages and love the current ability to change to any language with a swipe (longer or shorter, depending on their position in the list).

However, one possible solution to your issue that would work for people like me would be to avoid cycling through the whole list more than once: once you reach the last language you can keep on sliding your finger as long you want, the last language in the list will remain selected. If you scrolled too far, just slide back a bit to a previous language, as we can do now.

In this case one approach can be implemented: if only two language is enabled, only one language would be changed in one slide.
Otherwise it would cycle the three or more languages.

While that approach could work, it is limited to the cases where just 2 different languages are used in HeliBoard. It would probably require some preliminary check to see how many active languages there are before it starts switching languages. In addition, for the cases where a user has more than 2 active input languages, sliding too far could still revert to the initial input language, so the issue would remain for users with more than 2 active input languages.

I still believe that an option to stop cycling once the last language in the "active inputs list" is reached would be better. This would work regardless of how many input languages are currently active on HeliBoard. In the case of 2 active languages, sliding up would only show one other language (because that language is already the end of the "active inputs list"). In the case of 5 active languages, the input language would continue changing with further sliding up, up to 4 new languages, because that would be the end of the "active inputs list".

I still believe that an option to stop cycling once the last language in the "active inputs list" is reached would be better.

Yes, this would be a better approach.