Your problem is specific to MoodleCloud. In stock Moodle you can enter for example "en,de" in the field 'langlist' and your language selection drop-down will show exactly those two. If I understand right, in MoodleCloud its long list of languages are set through the config.php. You can not change that.
You should have raised the question in the MoodleCloud forum: https://moodle.org/mod/forum/view.php?id=8277. Hope a moderator will notice this and shift this discussion.
MoodleCloud
Shorten languages on language menu
This discussion has been locked so you can no longer reply to it.