While I think that motivation for any student is tough to explain I will outline several processes/methods below that support ESL students in your classroom environment. These methods might help ESL students increase their learning motivation to meet academic learning outcomes or targets. 

• Make a genuine attempt to learn and pronounce their names, this shows that you are empathetic to their culture, language, etc.
• Learn (genuinely) a phrase or two or three in their language. HI, Hello. Good Day, How are you?, etc. This shows you embrace their culture, language. ESL students can feel isolated if they feel their language or ethnicity is seen as a deficiency or defect.
• Outfit/decorate the classroom with items that make reference to their language, countries, food, flags dance, holidays, etc.  
• Employ lots of cooperative groups as many cultures see the group more as a value than the individual. Individualism is not tolerated in many cultures.
• If the ESL students have very low English language skills have them use bilingual native language dictionaries to complete assignments. This helps and supports their language frameworks. Just because they do not speak English well does not mean they in abstract terms.
• Use LOTS of gesturing to explain concepts. But, some gestures have universal meanings but be cautious of gestures that can mean something else in another language.
• ACT out concepts/lessons with motion, physical responses, simulations, and hands on learning.
• Pair up low level ESL students with a language buddy if possible, this helps them gain confidence in the classroom. But, still expect them to make an effort to learn material.
• Never call on a very low level English speaking student unless they really want to answer a question. If they insist let them but do not call on them randomly unless you have practiced an answer previously with him or her.
• Get to know their families customs, beliefs, religions etc, It might help you with class instruction or address behavior.   Ex, In Mexican culture, it is not acceptable for children to look you in the eyes or ask them to look you in the eyes when talking to them.

Here is an ESL/ELL linguistic resource to use with ESL/ELL students. 

Linguistic Accommodations for Scaffolding Instruction

Please consider these practices when working with ESL/ELL students.  I know there are more processes out there. I would be interested in knowing what other practices you use as an ESL teacher. Please add them in the comments section. Thank you.