D&D 5E How to Handle Characters That Can't Speak Language of Friendly Humanoids

[Swarmkeeper]

How about using Insight to determine if the communication is understood?

Insight. Your Wisdom (Insight) check decides whether you can determine the true intentions of a creature, such as when searching out a lie or predicting someone's next move. Doing so involves gleaning clues from body language, speech habits, and changes in mannerisms.

Possibly, but the PHB pg. 178 also indicates:

Other Intelligence Checks. The DM might call for an Intelligence check when you try to accomplish tasks like the following:
- Communicate with a creature without using words

 

[jasper]

Have the characters talk slower and louder. That always seems to work.

can you understand me now. evil dino behind you.

 

[Shiroiken]

Possibly, but the PHB pg. 178 also indicates:

Other Intelligence Checks. The DM might call for an Intelligence check when you try to accomplish tasks like the following:
- Communicate with a creature without using words

I would actually suggest using the variant of skills with different abilities, using Intelligence/Insight to send a message, and Wisdom/Insight to understand one.

 

[ArchfiendBobbie]

can you understand me now. evil dino behind you.

A wnewch chi roi'r gorau i gynnau cyn i chi ddigofaint y duw deinosoriaid?

I used Google Translate for that, so I probably just said I like dancing on tables and have an angry dinosaur in my pants.

 

[ExploderWizard]

Comprehend languages and tongues are still spells in 5E (I just checked) so whats the problem? Failing that, good old gestures & pantomime are fun to role play.