In order for any language to grow, "speakers" should be competent in creating new constructions. Therefore, a certain
language logic is required. Creating an extensive glossary is important but setting language rules is even more important. Those behind in-game languages like Arka and Darkmoon may already have all this in mind, I really know little of how advanced these projects are beyond what's been stated in this thread, but just in case, you may find these questions useful:
How does the language specifies inflections of gender and number?In English, for example, the particles "-s", "-es" and "-ies" are used on nouns for the regular plural form, and the suffixes like "-ess" to specify gender. Adjectives and verbs do not suffer any change in either case. In Spanish, every word suffers some sort of change regarding gender and number: verbs, nouns, adjectives, and so on. So, how does this work with the Stonebreaker and Enkidukai tongues? I can use the word "tabei" for 1 friend. Is it "tabeis" for 2 or more? Same with the adjective "kera" (dear) in Stonebreaker. I can say "Kera Indygo", can I say "Kera Indygo and Einnol" or "Kera Zorbels" (with no distinction of number and gender)? The word "urpnam" means warrior in Stonebreaker. What's the plural form? "Urpnams"? Stating these rules of inflection will allow players to use the language in a more flexible way.
How does the language conjugate verbs?Maybe we don't need to specify all grammar tenses. That would be a LOT of work. However, how verbs work for the imperative form (used to give commands such as "(you)Shut up" or "Let's go") may come in handy. This could be very simple if we already have a list of verbs.
How do syntax and word formation work?English is a language of word order. In plain, that means that the word that preceeds another modifies it. So, if we want to refer to a sword that is heavy we say "heavy sword". It's a very simple way to interconnect words and meanings. This can be used to combine particles of the language. For instance:
bonnhetolo - good for you
phonweh - place
bonnphonweh - good place?
The same can be applied for word formation. For example, using the word "urpnam" again and the particles (which I just made up for this particular example) "hrjun" for "group" and "Virr" for "leader":
urpnam - warrior
hrjunurpnam - army?
urpnamvirr - war lord?
Again, these are just some suggestions. If we know how the languages work, a glossary will allow new combinations and player can use their own competence to use them and understand them.