Learn Danish: Rejseguiden er ikke troværdig medmindre den beskriver alle problemerne. - The travel guide is not credible unless it describes all the problems.

It combines the root tro (belief, faith, or trust) with the suffix -værdig (worthy of). This literally means "worthy of trust", which translates to credible or trustworthy.

Does troværdig change if we describe a neuter noun or a plural noun?

Yes, adjectives ending in -værdig follow standard adjective rules. You would add a -t for a neuter noun (like et troværdigt rygte) and an -e for plural or definite nouns (like troværdige rejseguider).

Does the conjunction medmindre trigger a change in word order?

medmindre (unless) is a subordinating conjunction, so it starts a subordinate clause. This means the subject correctly comes before the verb (den beskriver). However, keep in mind as a B2 refresher that if you added a central adverb like faktisk (actually), it would have to go before the verb in this clause: medmindre den faktisk beskriver.

Why do we use the definite plural problemerne after alle instead of just problemer?

In Danish, using alle with a definite noun means "all of the [noun]" for a specific group. alle problemerne means "all the problems" (specifically those related to the travel guide), whereas alle problemer without the definite ending would mean "all problems" in a general, universal sense.