Open the movie and tap the music note icon or "SW" decoder option to view and select from the available language list.

Here are some popular dual audio movies sites:

Ability to select from dual audio tracks from files - VirtualDJ

If you choose to use free sites, you must navigate a minefield of malware and fake links. Follow these three golden rules:

The demand for isn't going away. However, the landscape is shifting. Pirate sites face constant domain seizures (Government blocks hundreds weekly). Meanwhile, services like Amazon Prime are making dual audio mainstream.