When user register his account and he uses Latin symbols,
then his name will go to SQL base as 1 symbol registration to 1 symbol in SQL.
When user register his account and he uses NONE Latin symbols,
then his name will go to SQL base as 1 symbol registration to 2 symbol in SQL.
That mean that automatically his username is divided by 2.
And will be not 25 symbols but 12 symbols.
Why not chage user_name varchar(25) by default to bigger value???