Translation:We always buy chocolate in Belgium.
Yes, "en" means in Belgium in this example. "En" goes before feminine countries or masculine countries beginning in a vowel: en France, en Inde, en Angleterre.
"Au" goes in front of masculine countries: au Maroc, au Canada, au Kenya.
And a masculine country beginning with a vowel: en Uruguay
Achetons is typically pronounced "ash ton," though sometimes I've heard it pronounced "ash eh ton" with the "eh" barely enunciated.
If you are ever curious about how a word is pronounced, I recommend https://forvo.com/.
Here you can hear a variety of native speakers pronouncing "achetons".