Here are my favorite books on linguistics.
If you are going to teach languages, it's important to understand what language is all about!
These books talk about what language is, how it is learned, and how it is taught.
Words are put together in sentences according to rules.
Steven Pinker explains how with depth of understanding and humor.
He uses regular and irregular verbs to show that there is a
a system in the brain that applies rules to produce correct utterances.
Inspect/Order Words and Rules: The Ingredients of Language from Amazon.com
Language, by Edward Sapir was my first book on linguistics. I still have my original one, from around 1958.
A real classic book for those interested in languages.
First published in 1955. Very readable.
Inspect/Order Language from Amazon.com
If you are serious about teaching languages, you must buy this book and read it carefully.
It explains clearly the various methods that are used in teaching spoken languages.
It does not judge or criticize. It lets you decide for yourself which of the methods you will use.
You may want to use a little of each method.
Inspect/Order Techniques and Principles in Language Teaching from Amazon.com
I have the sixth edition. I can only assume that the 8th edition is even better.
This is an excellent book on linguistics, the science of language.
If you are going to buy only 1 book on linguistics, this can be the one.
It is very clear and does not waste any time criticizing other linguists.
It's isn't really about teaching languages, but you need to understand this before you teach ...
Inspect/Order An Introduction to Language from Amazon.com
An excellent reference to the romance languages.
It discusses Latin and the similarities and characteristics.
of languages which descended from Latin. (French, Spanish, Italian, Portuguese, Romanian, Catalan, Occitan, Rhaeto-Romance and Sardinian)
Each chapter is an essay written by a different person, so the ability to directly compare
the languages is limited.
Inspect/Order The Romance Languages from Amazon.com