prevent user from changing language?

[Khalat Jalal]

I have a question, I want to prevent users changing the language and or web site theme, how to do that?

[TSP]

For the language you would have to disable it, which would also mean it'll not be available for you as an administrator either, unfortunately. Customization > Languages > Click on where it says "Enabled" for the language you wish to disable. The language pack where it says "Locked" means it's the default language and you'll have to change to another default language before you can enable that. 

For themes you go to Customization > Appearance > Themes. Click on the pencil icon (Edit) for the theme you wish to make unavailable for members and then change the setting "Available for" under the "General"-tab to what you want.

[Khalat Jalal]

 Thank you @TSP It was usefull, I was used vbulletin before, there was an option that disables user to change language or theme, it is one of my wishlist for IPS to add it in the future release .