You have to select Language option from SAP Logon.
1st login: if keep blank Language on Sap Logon, system normally get default from your account in T-code SU3 (almost it's English 
)
2nd login: select your French => you can maintain wt text in French. ... etc.
Good luck.
In SE11, you can see table T512T, there is field Language Key there => of course you can maintain multi language for your wt.