It really isn't. I've spent a lot of time trying to tune langmap/keymap and looking into other options but the result is mostly unsatisfactory. Some of the issues: only translates the first letter of the command; doesn't support :commands; isn't expressive enough to remap punctuation.
Vim needs to be keyboard layout-aware in order to support non-Latin keyboards. It also needs to know whether the current input state is expecting text or a command (e.g. typing ":s/" from the normal mode should always be parsed using the Latin layout but the currently active input language should be used following the "/").