warning: file_get_contents(sites/default/files/languages/ar_bb3f64e1d3c493008e8d5eee5511c741.js)

I was getting the same error occasionally on a multi-lingual site as well, though not consistently. However, when i disable the "Optimize JavaScript files" option under admin/settings/performance, the problem appears to go away, at least on my site. Turning that off isn't ideal, but might give you a workaround.

Perhaps there's a conflict with the javascript caching/compression system and the language modules. The i18n module says it doesn't work with aggressive mode caching, but i had page caching set to "normal" or even disabled and was still seeing the problem until i turned off the javascript optimization.

this is a bug in progress #338630: Locale is unable to rebuild lost Javascript translation files

but you can solve it without applying any patch
just install the module attached to 338630#comment-2035162
then visit admin/settings/language#js-translations
and submit the button over there