Problems with langauges

Hello!

I've made translation of Gallery2 Checkout module and made it into .po and .mo files. And well my problem is that the gallery keeps changing the language sometimes when the site reloads. Its not every time it does that, but sometimes. Every 5 or so reloads it changes all the text of that Checkout module back to English again, then with the next reload its Finnish again. I can't think any reason why it does that. I know that by hard coding, manually modifying the files I could solve this problem, but is therea any other ways to solve this?

Thanks in advance!