javascript not return value how to solve?

[finish2023]

my code :

obj={"法语":"french","西班牙语":"spanish","德语":"german","日语":"japanese"}
var res=null
function get_language(k){
if (!(k in obj)){
return 'english'
}else{
return obj[k]
}

}

var res=get_language("阿拉伯语")

browser is run success

 

[Phoenix78]

return try

 

[finish2023]

return must in function