AllegroTrans' comment above is spot on, there is no direct translation going by google search results.
I agree with the use of the term summons since it has long been translated this way and after a cursory review of the ways in which legal proceedings can be launched in France, Luxembourg and Belgium one can safely say that it is analogous with assignation (or in Bel. 'citation').

What to do then with the adjective 'commerciale'?
In the 3 French speaking jurisdictions mentioned above the instrument known as an 'assignation' is the same no matter which branch of law or which level of the judiciary is considered. We should be careful therefore not to introduce by our translation a distinction which does not exist. Translating it as 'commercial summons' would suggest, to myself at least, that there could exist in Luxembourgish law that some particular form of summons does exist - I would, lacking any knowledge on the subject, assume that it meant a summons for a specific type of procedure with specific rules adapted to the commercial world (less time to prepare, different rules for default judgements, different rules relating to appeals etc.). After a good deal of research online I have concluded that no such unique instrument and procedure exist.

The adjective 'commercial' seems intended merely to communicate that the affair is a commercial one and that the rules of commercial law will be applied and this before a commercial judge i.e. the legal proceedings are not different save for a few changes necessitated by the change of the branch of law (il s'agit encore du régime procédural du droit commun apart quelques dérogations législatives prévues en matière commercial comme par exemple les règles applicables à la preuve).

I would therefore translate the whole thing as a 'summons to a commercial hearing' , 'summons to appear at a commercial hearing' or alternatively 'summons to appear before the Circuit Court of Luxembourg Province, Commercial Chamber'. Though the first sounds better to me.

I have, however, two caveats.

1st caveat.
Summons to + a commercial hearing returns very few meaningful results in google so although it would be understood readily by english speaking jurists it might not be the term they would use.

2nd caveat.
Nikki Scott-Despaigne, commenting above noted that 'commercial summons' would be appropriate - she seems to have a great deal more experience than myself so perhaps the asker might want to go with her comment though I don't know if she proposed it with much confidence but I imagine be understood - my development above might be a splitting of hairs.

At any rate I think my translation is at least a useful one and would sit nicely with 'summons to an interlocutary hearing' as a possible translation for the preceding sentance (I would be interested to know how the asker got on in both cases, by the by). So in case it might help here it is and hopefully some more people will be able to weigh in soon.
Good luck at any rate


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Note added at 4 days (2017-08-07 17:12:49 GMT) Post-grading
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Two things I forgot to mention, Luxembourg while it has commercial judges does not have a 'tribunal de commerce' hence I mentioned 'Circuit Court of Luxembourg Province, Commercial Chamber'.
See: http://www.justice.public.lu/fr/organisation-justice/juridic...

Secondly, for information on 'assignation' I consulted the followong book on google books: https://books.google.ie/books?id=5cWsCwAAQBAJ&pg=PT130&lpg=P...