"MULTi18" means the game contains 18 languages. You can usually change the language:
A file labeled part2.rar is useless without its counterparts. You must ensure you have downloaded: Half.Life.2.Episode.One.MULTi18.part1.rar Half.Life.2.Episode.One.MULTi18.part2.rar
Half.Life.2.Episode.One.MULTi18.part2.rar (The one you have) "MULTi18" means the game contains 18 languages