'TEFL' has two possible pronunciations:
- [ˈtef.əl]: with a schwa
- [ˈtef.l̩]: with a syllabic1 L
The reason Anglophones insert a schwa is because the tautosyllabic coda cluster2 */-fl/ is not found in English (Phonotactic Constraints) and native speakers are unfamiliar with that cluster so they insert a schwa there or make the L syllabic. If it were */tefl/ (single syllable), it would violate the phonotactics of English.
NOTES:
- Syllabic consonants are consonants that are capable of making a syllable on their own. In English, /l m n r/ can be syllabic when they come right after an obstruent (/p t k s g f/ etc) in an unstressed syllable for instance the second syllable of button is usually pronounced as a syllabic n (not every individual pronounces it with a syllabic n though)
- 'Tautosyllabic' means being the same syllable, for example, the n and t in ant are in the same syllable so they're tautosyllabic. 'Coda' refers to the consonants after the nucleus (usually vowel) of the syllable (e.g. nt in ant). According to English Phonotactic Constraints, English doesn't have OBSTRUENT + SONORANT in the same syllable in the coda. (Obstruents: p, t, k, s, k, f etc. Sonorants: l, m, n etc.) Note that this is entirely different from OBSTRUENT + SYLLABIC consonant sequence.