Note that this only seems to disable the dropdown in your page, not in the users profile unfortunately.
what can i do for this? i would like disabling for all users
Remove all other language packs, so the site only uses the one language.
is there another solution?
There are probably several,
Helen gave one previously, I've given another, a third would be to edit your theme files so the language menu doesn't show. But if you are not using the languages, I'd still recommend removing the language packs anyway.
Perhaps if you are still looking for other solutions you can tell us exactly what the issue you are trying to solve is and why the solutions already presented don't work for your needs.
Search in the administration block for the "langlist" option and enter there one language.