"We order you to learn Dutch."
Translation:Wij bevelen jullie om Nederlands te leren.
"Het" would be used in a context such as when ordering someone to speak in Dutch. Here, we aren't being asked to learn in Dutch. Think of it as literally "to speak in the Dutch (language)" or "to write in the Dutch (language)". For example, "Zeg het in het Nederlands" ("Say it in Dutch", literally "Say it in the Dutch (language)") or "Schrijf het in het Nederlands" ("Write it in Dutch", literally "Write it in the Dutch (language)"). Funny enough, this tiny bit of grammar is kind of similar to Russian where you'd say "Скажи по-русски" ("Say it in Russian", literally "Say in Russian (language)") compared to "Учить русский" ("Learn Russian").
There are certain verbs that require the use of om and/or te + infinitive constructions. Bevelen would be classified as an Om-Verb (i.e. a verb that governs the use of om).
However, there are certain verbs that allow for the omission of om; bevelen is one of them.
Read here for more insight into the verbs that require such additional components.
Feel free to ask me directly for more help! \^_^
And the certain auxiliary verb in different sentences will require different prepositions. When the preposition is one of the group to start a subclause it appears te+infinitive. There is om verb list for the verb that can omit the om, but there is no om verb list to tell you what vert is om..te + infinitive. Literally you just need to know the te verbs list and om verbs list, then you will have to know what verb need om as preposition.