I am very interested in teaching my 10 month old English. Our native language is Dutch and there are a lot of phonemic similarities with the English language, since they belong to the same language family. I am worried that teaching him English before he has mastered Dutch will lead to a lot of confusion an ultimately do him more harm then good.
So I can’t speak for English & Dutch but we have introduced multiple languages with success & perhaps that will encourage you.
We speak English (& Scots!) but live in a Spanish country & we taught our now 5 yo son both from birth. He switches easily between them, reads both fluently, Grade 1/2 level. He never has had a problem recognising which language is which. I think you would do your son a bigger disadvantage NOT to introduce another language early than to wait till later, just in the sense that you are missing that wonderful window when they don’t so much learn as absorb. Our 2 year old sometimes makes up her sentences with a bit of both but that will sort itself out soon enough. A small price to pay for eventually being eloquent in 2 languages!
My son never showed me he could read as a baby, he spoke the language long before he could read it but the investment early on was well worth it. I think if you introduce it early enough they are familiar with the similarities & differences between languages long before you give them credit for it.
In addition we introduced French early on & now do Latin & greek a few times a week as well without any problem/ confusion for our son. In fact he loves seeing the root word connections between the languages.
I learned Lithuanian and English, with German as a third language exposure. And I started talking (in whole sentences) before I was 1. It was only later, when I more or less lived with English as a main diet of language that I lost the German (the relatives who spoke it moved away), but the Lithuanian stayed with me, and even now, I still can understand about 90% of anything said to me or that I read in Lithuanian, despite not being near Lithuanian speakers on a regular basis for more than 30 years. (I do have difficulties talking in it nowadays).
The people you meet that are deaf only need you as an interpeter or someone to speak for them in an emergency situation. It is not a language that is needed on a daily basis that will benefit you for a job, such as spanish does (unless you are working with deaf bosses). Second disadvantage is that the American Sign Language is not speaking english but rearranged english that is not normal conversation to the average hearing person, as it states http://researchpaperwritings.net/and[url=http://www.dartmouth.edu/~news/releases/2002/nov/110402a.html]http://www.dartmouth.edu/~news/releases/2002/nov/110402a.html[/url]. It is hard for a hearing person to learn to talk “backwards” learning their language.