American Sign Language
If you only learn one sign, let this be it. It says I Love You.
WELCOME
My 8 year old granddaughter is a disabled child with special needs.
She can hear and understand, but does not speak. We are learning to sign with and for her. It's a good second language for ANYONE to know.
The ASL Alphabet
There are also gestures for WHOLE words as the following shows...

MORE and ALL DONE
Thanks
And one of my favorite words, Grandma.
These are only 4 examples of signs for whole words. There are places on the web and many books where you can learn whole words. Some colleges even have evening classes where you can learn more.