Yes, we can almost certainly break this, given enough ciphertext.
One approach would be to use a dictionary and use word patterns. For instance, if the ciphertext word is qddxfozogf, then the plaintext word was probably ammunition. Notice how the 2nd and 3rd letters are the same; and the 5th and 10th letters, and the 6th and 8th letters? The word ammunition is essentially the only word that has this special pattern. One could expect that some fraction of words will be essentially unique, in their pattern of repetition. With enough ciphertext, you'll be able to uniquely recover one or more of the words, and then the rest of the cipher will be easy to break.
Frequency analysis will also almost certainly be possible. For instance, the letter q occurs with frequency 0.1% in English, 0.02% in German, and 0.9% in Spanish. In contrast, the letter e occurs with frequency 14.7%, 17.4%, and 13.7% in English, German, and Spanish, respectively. Therefore, if you choose uniformly at random between English, German, and Spanish, the letter q will occur in the plaintext with frequency about 0.3%, while the letter e will occur with frequency about 15.3%. Notice how e is still much more common than q? This indicates that frequency analysis remains possible. (Wikipedia has data on the frequency statistics of different languages.)
Digraph analysis (the frequency of pairs of letters, like the pair th or qu) will also almost certainly be possible.
Finally, there are more sophisticated methods for cryptanalysis of simple substitution ciphers, such as hill-climbing. These methods will almost certainly be effective at ciphertext-only cryptnanalysis.
And the cipher will completely fall apart in the presence of known plaintext (let alone chosen ciphertext).
TL;DR: Your proposal is highly insecure. Don't use it.
