In compliance with applicable laws on the use of languages, "French, German or Luxembourgish may be used" for administrative and court matters.
For Court matters
Luxembourg's three official languages may be used in the country's courts and tribunals. No one of the three languages takes precedence over any other. In practice, however, discussions and hearings are usually conducted in French and/or Luxembourgish. The use of German is less common. This is a matter of a usage and not a legal obligation. On the one hand, because a large number of lawyers today are French-speaking and, on the other hand, because Luxembourg laws and legal deeds (the writings of lawyers, court rulings, etc.) are written in French. The use of any of the other official languages is however possible. In criminal matters, the decisions handed down by judges often repeat citations from reports by the Grand-Ducal Police that are generally written in German.
For professionals in the legal sphere, the use of French, German, or Luxembourgish does not pose any problems: The law in fact requires all lawyers and trainee lawyers registered with the Luxembourg or Diekrich bar to master the three administrative languages of the Grand Duchy. The is also true for judges, who are required to demonstrate adequate knowledge of these three languages prior to their first appointment.
Comprehension problems occur when individuals appear before judges and do not master any of these three languages of the country. Such a situation may arise for individuals who have chosen to defend themselves personally in court—when the law does not require them to be represented by a lawyer—or for individuals who have been summoned to serve as witnesses.
When such individuals are not able to make themselves understood by the judge in one of the three languages of the country, their explanations must be translated. For these reasons, a sworn interpreter must be called to the hearing. For civil matters such as dismissals, divorces, rental contracts, etc., it is up to the party requesting the appearance of a witness who does not master any of the country's three languages to inform the court of the need for an interpreter. This party must then advance the costs of the interpreter, which they could possibly recover from the opposing party, if the latter is sentenced to pay the costs and the expenses of the trial.
In criminal cases, if the summoned person or witness does not speak French, German or Luxembourgish, the prosecuting authorities—the prosecutor—would usually handle the hiring of an interpreter.
The rules described above also apply for any materials written in a language other than French, German, or Luxembourgish: if a party wishes to rely on such documents, they must provide the judge and the opposing party with copies of the documents, together with their translations (generally into French).
In practice, documents in English (for example, a contract) may be submitted without translation, given that Luxembourg judges also are competent in English.
For Administrative matters
A citizen may formulate their petitions in one of these three languages, and the administration must use, insofar as possible, the language chosen by the petitioner for its response. In practice, French is favoured for written language and Luxembourgish is favoured for spoken language (for work and communication). Administrative deeds are drafted in French and "only the French language shall prevail" applies at all levels of public administration.