One of the most common questions people ask when it comes to TEFL courses in Spain is whether they'll be able to successfully carry on with their lives and be a good TEFL teacher without the knowledge of the local language, Spanish.
Let's get something straight out of the bat. Knowledge of Spanish is not necessary to become a TEFL teacher in Spain. In fact, conversations in Spanish are highly discouraged in classrooms, so as to inculcate a sense and habit of English fluency and reduce the incidences of fallback to the native language during pauses and conversations.
That's not the whole story though. Spanish is the lingua franca of the Iberian country and everybody speaks in their native tongue, with very few folks fluent in english. So if you want to survive in the big city and carry out your daily tasks without much hindrance, at the very least, basic knowledge of Spanish is crucial.
Even in classrooms, with most of your students being native Spanish speakers, knowing your way around the syntax, pronunciation and grammar of Spanish can greatly help you in teaching a new language, I.e. English. This knowledge can help you develop your own teaching style and technique while personalizing/attuning yourself to the skill sets of your students.
For instance, most Spanish speakers struggle with words with strong t, such as comfortable, vegetable, etc as well understanding the difference between homonyms like rain/reign, similar words like bear, beard, beer, etc. The grammar of Spanish also is quite different with no place for words like "have". This can make teaching tougher since they've never encountered such a way of speaking or using verbs in a normal sentence.
Then, there are " false friends ", words that are present in the both Spanish and English but mean different things such as constipacion which means a common cold rather than bowel difficulties as expressed in English . This could make your classes difficult if you don't understand the Spanish counterpart and lead to confusion among the students.
There will be times though when students might rely too much on your Spanish skills, which you need to be aware of. For example, don't let them ask a question in Spanish but encourage them to try asking it in English.
However, As you learn a new language, you'll come to understand the struggles of your students and empathize with their difficulties which can only make you a better teacher.
Employers and businesses also require you to have some knowledge of Spanish since you'll be dealing with clients, colleagues or in school, parents, all of whom are most comfortable with Spanish.
Knowing the language of your country also has many practical uses and opens up doors to the new culture and community, allowing you to make new friends and enjoy your day to day life. So learning Spanish is always advisable if you're moving to Spain.