db.ara.drop();

// http://en.wikipedia.org/wiki/Arabic_verbs
db.ara.insert({ _id: "past_writes", t1: "كَتَبْتُ" });
db.ara.insert({ _id: "present_writes", t1: "أَكْتُبُ" });
db.ara.insert({ _id: "future_writes", t1: "سَأَكْتُبُ" });

db.ara.ensureIndex({ t1: "text" }, { default_language: "arabic" });

db.ara.find( { "$text" : { "$search" : "كتب" } } )

db.ara.find( { "$text" : { "$search" : "كتب", $language : "arabic" } } )
Error: error: {
        "waitedMS" : NumberLong(0),
        "ok" : 0,
        "errmsg" : "$language specifies unsupported language",
        "code" : 2
}