have you tried searching it with case sensitive?

i searched in language there no "log in" 

Omer, Do blank search in the Facebook connect plugin's section, in the search result you can see all the values of Facebook connect plugin.

{text key='fbconnect+connect_btn_label'} is the text key you are looking for.

See screenshot:

i found theme develeper said me it s a pic 

i changed pic in themplate images directory

Okay, good to hear.

Is you issue resolved by changing the picture?

yes resolved

Great.