Welcome,
You can use a global multidimensional array, like this: uJZQqb - Online C++ Compiler & Debugging Tool - Ideone.com
Then have another variable holding the current user language id (between 0 and 2), and use this variable as an index of the first dimension of this multidimensional array
lcd.createChar( 0, languages[user_language][0] ); // create character 'a'