Since Luxembourg is surrounded by other countries in such close proximity, the European kosher list's are very helpful.

Allowed fish
Liqueurs

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