To become an Air traffic Controller, all you need is a “fin d’études secondaires” diploma or an equivalent diploma.
You can find out if there are any vacancies on this homepage of the government.

To apply as “fonctionnaire de l’Etat” you either have to pass a classification exam or you can apply as “employé de l’Etat”. Anyway you will have to pass the FEAST test and a medical exam.

Successfully passed this test, you will start your training at the DFS (Deutsche Flugsicherung) in Langen (a few kilometers away from Frankfurt am Main)  where you will acquire the necessary theoretical and practical skills to start your on-the-job training in Luxembourg. The training in Langen will last 12-16 months. During these months, accommodation and salary will be provided.

Back in Luxembourg, you start your practical on-the-job training in Luxembourg which will last for about 18 months.