have you had a look at the Youtube Embedded Player Documentation ? It seems the hl parameter is only supported for the HTML5 and AS3 players. This may also help:
Make captions automatically appear for an embedded video by adding "&cc_load_policy=1" to the video's embed code.
You can also choose a caption language for the embedded video. To specify the caption language for the video that you'd like to embed, just add "&cc_lang_pref=fr&cc_load_policy=1" to the video's embed code.
"cc_lang_pref" sets the language for the captions shown in the video.
"cc_load_policy=1" turns captions on by default.
"fr" represents the language code for French. You can look up 2-letter language codes in the ISO 639-1 standard.
Hope it helps
... View more