Since Luxembourg is surrounded by other countries in such close proximity, the European kosher list's are very helpful.
Belgium:
Shomre Hadas
Cyprus:
Cyprus Jewish Community Center - Chabad Lubavitch of Cyprus
France:
Beth din de Paris
Germany :
Ord
Grecce:
Chabad Lubavitch of Greece
Hungary:
Lubavitch of Hungary
Italy:
Italy Kosher
Netherlands:
NIK organisation of the Jewish Communities in the Netherlands
Norway:
Va'ad HaKashruth
United Kingdom:
Beth din de Londres
Spain:
Kosher Product List Chabad Barcelona
Comunidad Judia de Madrid
Switzerland:
Communauté Israélite de Lausanne
Israelitische Gemeinde Basel
Israelitische Religionsgesellschaft Zurich