Is it true that you need to know Spanish in order to live in Texas?

No. The people living in the areas you named are usually bi-lingual (which is a good thing no matter where you live). English is required to attend school, get a job, etc. I speak English everywhere I go along the border, and 99% of the time get responses in English. Texas didn't "allow itself to be messed with". People who refuse to learn English are at a great disadvantage, and Texas does not encourage anyone to speak Spanish and not learn English. ?Me entiendes?