Sekai Camera supports the following 7 languages: Chinese, English, French, German, Japanese, Korean, and Spanish.

On your iPhone, please go to Settings > General > International > Language to select a language. Once a language is selected, the menu and messages will change into the language of your choice.
There are no limits to the choice of language when you input text (i.e.: on text Air Tag posts or your profile registration). Languages other than the 7 mentioned above are not supported by Sekai Camera.