I've translated many strings of the wp theme using pll__ or pll_e in php files
Static strings should be translated with __() or _e() (and translations managed by .po/.mo files) rather than pll__() and pll_e() which are made for theme options.
That's a pity that themeforest accepts non internationalized themes. It makes it useless for more than a half of WP users.
How is your enqueued your javascript file?