Students’ mother tongue may in one way or another influence their ability to pronounce particular sounds in foreign languages and this is often the main reason why some students speak English with a really strong accent of their native language.
The sounds that don’t exist in other languages are usually the greatest problem for students of English because it can be extremely difficult for them to understand and learn how to articulate these sounds.
Though this list may vary between speakers, here are the five English sounds that are most frequently regarded as exceptionally difficult to learn:
1. TH or /θ/
The sound /th/ as in thing, thought or theater, doesn’t exist in many Germanic, Romance and Slavic languages. This is why European students of English often have difficulties with it.
Though this sound can quite easily be pronounced in isolation, speakers often find it difficult to use it correctly in a word so it wouldn’t resemble /f/, /s/ or /t/. In Cockney, which is one of the most widespread non-standard dialects in England, the sound th is almost completely replaced it by /f/ in medial and final positions and with /t/ in word-initial positions.
This video by Fluency MC may help you understand the complexities:
2. DH or /ð/
Similar to the previously described /th/ sound, /dh/ sound may also cause a lot of trouble for an ESL learner. Dh appears in the words such as this, that or they which are very frequent.
Its manner of articulation largely resembles that of the sounds /z/ and /d/ and this is the main reason English learners find it difficult to pronounce it correctly.
In Cockney, this sound is completely replaced by /v/ in medial and final positions and with /d/ in initial ones.
3. R – /r/
The sound /r/ is problematic for many non-native speakers of English because its manner of articulation and use differ among varieties of English. The most important difference is that RP and GA speakers don’t pronounce /r/ in same contexts. While the RP speakers don’t pronounce it in word-final positions or after long vowels, in GA this is not the case.
Furthermore, features of this sound vary geographically. Scottish people, for example, pronounce a very strong /r/ in front of /l/, /m/, or /n/. This is called rolled r (trill) and is regarded as a completely different phoneme from the alveolar approximant found in RP and GA.
4. H – /h/
This sound is frequently considered to be one of the hardest English sounds because of its peculiar manner of articulation and the fact that it doesn’t exist in some Romance languages.
French speakers are usually unable to pronounce this sound, so they often completely omit it from the word. Its articulation is so difficult for them that they cannot even find a substitute for it.
5. L – /l/
English l has several different manners of articulation depending on the surrounding phoneme context. Thus a word-final l won’t sound the same as a word-initial one. What’s more, to a non-native speaker it may even sound as a completely different phoneme.
The two ls in words bottle and lane are interchangeable but their proper articulation can often cause troubles for ESL learners.
This is especially related to Chinese speakers who have a single alveolar consonant for both of these sounds.