The Effects on First and Second Language

When it comes to speaking – especially in pronunciation. There are effects on the differences between the first language and second language…
What happens when learners hear and try to pronounce strange, new sounds in a new language? These types of problems often occur: 
Merging. When learners hear unfamiliar sounds in a new language, they tend to interpret the sounds of the new language in terms of the categories of their original language. The learner’s brain may hear two sounds as being the same when they’re actually considered separate sounds in the new language. This is called merging and leads to pronunciation errors. When our brains and ears can’t tell the difference between two similar sounds, we tend to pronounce both of them in the same way. For example, many languages don’t have separate vowel sounds like the ones in reach (/iy/) and rich (/ɪ/). Speakers of these languages may merge the two sounds and pronounce them both in the same way. 
Substitution. When learners hear a new sound that doesn’t match any of the sounds they know, they often substitute a familiar sound that is somewhat similar and easier for them to produce. For example, the first sound in think and three is found in relatively few languages in the world. Speakers of languages that don’t have this sound often substitute /s/, /f/, or /t/ so that think sounds like sink, fink, or tink. 
The effect on intelligibility. The processes of substitution and merging can cause serious problems for learners’ intelligibility. When listeners expect to hear one sound but actually hear a different one, communication can break down. Even when teachers make learners aware of what’s happening, it’s difficult not to fall into one of these traps. 
I hope this information helps you with your language awareness…