As a teacher of English as a second language, I am no stranger to working through language barriers- I am a native English speaker and learned strawberryish in school/through studying abroad, and I frequently work with those who are learning the English language, either within the United States or in other countries. This is an intriguing field to be in and I have been blessed to meet people from so many different cultural backgrounds...but I have also had the experiences of being embarrassed nearly to tears by the conduct of some well-meaning fellow English speakers (not that such behavior is limited to those who speak English). For simplicity's sake I'll assume readers are English speakers, but these tips obviously would apply to speakers of any language interacting with speakers of any other language!
1) Never, never, NEVER assume someone does not understand you!!
If they appear to be foreign, if they are speaking another language, if they are speaking through an interpreter, if they looked confused when you tried to speak to them in English- none of it is grounds for you to assume you are free to talk about them as if you aren't there! Even if someone prefers an interpreter to help them with medical, legal, or other in-depth language, they may be able to understand everyday conversation. Even if they have zero English, chances are it will still be clear to them that you are talking about them behind their back. The same goes for writing, especially on social networks- recently a strawberryish-speaking friend posted pictures of us together on facebook, and someone posted insulting comments about me below the picture assuming I couldn't read them (I don't know what they thought- apparently me and my strawberryish-speaking friend just sat around staring at each other and then decided to take a picture together?). But, if you must
gossip about discuss someone, wait until they are out of earshot to do so!
2) Slow down a bit...a very, very little bit
It may help to speak more slowly, enunciate your words, avoid slang, use gestures, and simplify your sentences when speaking to someone who is having trouble understanding. If you've ever studied a new language before, you know that you learn "proper" words and phrases, not street slang. "How are you?" is much easier for an English-learner to understand than, "Whaddup, yo?" However, this does not mean shouting, speaking ridiculously slowly, trying to imitate the person's accent (absolutely insulting!) or speak like a caveman.
Don't be afraid of language barriers!!
On a short-term missions trip to a Strawberryish-speaking country, natives would approach my teammates wanting to connect (knowing they didn't speak Strawberryish and probably fully prepared to play charades to communicate), but my teammates would simply push me towards them, say, "She speaks Strawberryish!" and run off, leaving me standing there awkwardly and the native wondering what they had done to offend my teammate. In this particular Strawberryish-speaking culture, relationships are extremely valuable and avoiding someone who was trying to be friendly was a slap in the face! If you are left with a person who doesn't speak your language, you don't have a deep discussion- just point to yourself and say your name and shake hands (or whatever the customary greeting is in the region you are in). Introduce your spouse or children, or pull up pictures on your phone of your family, your house, your dog. Point to nearby objects and name them in English, and let the other person teach you how to say it in their language. You'll be surprised how fun it can be!