Is Vietnamese people's English hard to understand?
Japanese people's English is also hard for Vietnamese people to understand

I sometimes hear Japanese people who have just arrived in Vietnam say that "English doesn't work well with Vietnamese people." They have a fair amount of experience using English, yet they find the other person's English hard to catch, and their own English doesn't get across well either.

My Vietnamese wife's relatives say the opposite: "Japanese people's English is hard to understand."

Research on English as a second language contains observations pointing in a similar direction. A study conducted at an Australian university reported that, among listeners from various countries, Japanese listeners rated the English of Vietnamese speakers as harder to understand than other listener groups did (Nguyen & Ingram, 2016). Because the study was conducted in the context of Australian English, care is needed in applying it directly to Japanese-Vietnamese interactions. Even so, it offers a clue that Vietnamese people's English poses a particular listening difficulty for Japanese people.

When Japanese people speak English, they are pulled toward katakana pronunciation even without meaning to be. Mouth movements ingrained over many years cannot easily imitate native English pronunciation. A simple example is how "make" becomes "meiku" and "strike" becomes "sutoraiku." They tend to clearly pronounce consonants that should be barely audible.

In addition, Japanese is a language that keeps time in units called morae (beats), and each beat is roughly the same length. Japanese speakers are not good at the English way of intonation, which lengthens stressed syllables and shortens weak ones, and they tend to pronounce each word separately. The result is a rhythm in which the whole English sentence is flat and it is hard to tell what is being emphasized.

Because the number of syllables increases and the rhythm becomes uniform, it tends to reach Vietnamese ears as "too many syllables, with little distinction between strong and weak."

The same thing happens with Vietnamese speakers. When Vietnamese people speak English, they are pulled toward Vietnamese pronunciation even without meaning to be.

A simple example is "three" sounding close to "tree." Because Vietnamese does not have the English th (/θ/) sound, it shifts toward t, which is made in a nearby position.

Besides sound substitutions, there are several features that Vietnamese does not have. One is consonant clusters. Because their native language gives them no basis for pronouncing words like "street" or "strength," where three or four consonants appear in a row, consonants get dropped or a short vowel gets inserted between them.

Another is the handling of word-final consonants. When you pronounce "cat" in English, the final /t/ is made by touching the tongue to the roof of the mouth and then releasing air with a small burst. In Vietnamese, however, word-final stops are made by forming the mouth shape only and closing the sound without the final release. When people speak English with this habit, word-final consonants reach Japanese ears as "inaudible" or as "disappearing partway" (Cunningham, 2009). The word-final consonants that Japanese speakers rely on as clues to identify words are simply not being produced.

In addition, Vietnamese is a language with six tones. Each word is assigned its own tone, and the pattern of pitch determines the meaning of the word. When this sense carries over into English, rises and falls in pitch appear that differ from English intonation. A study analyzing questions in English spoken by Vietnamese speakers found that the less advanced the learners, the more they tended to use pitch movements resembling Vietnamese tones at the end of English sentences (Nguyen & Dao, 2018).

Japanese people's English gains extra syllables and its rhythm becomes flat. Vietnamese people's English drops word-final consonants and takes on the habits of tones. Because the ways they break down are nearly opposite, each side's English is hard to fill in using only the sense of one's own native language.

So far I have laid out the differences between Japanese and Vietnamese pronunciation, but reading this will not suddenly let you understand someone's English from tomorrow. What does change a little is how you put your mind to work when facing the other person's English.

When a Vietnamese colleague speaks English and there is a word whose ending you just cannot catch, if you can think, "Vietnamese doesn't release word-final consonants, so this person may be pronouncing /t/ or /k/ in a way that doesn't reach my ears," it becomes easier to guess the word from the flow of the conversation.

This is less about studying English and more about an inference that comes from knowing a little about how Vietnamese sounds work.

The same can be said of knowledge on the English side. I wrote earlier that "three" sounds close to "tree," but this is not limited to Vietnamese people's English. Among native English speakers, too, sociolinguists have documented pronunciations in which th becomes close to t or d, in New York City and its surrounding area, in Irish English and in some African American speech (Th-stopping). Historically, it is explained as having become established as a working-class way of speaking under the influence of the sound systems brought by Irish, Italian and Jewish immigrants from the 19th to the early 20th century.

I belong to a generation that had its th pronunciation strictly corrected at school. Even now, when th is pronounced close to t, I am tempted to think reflexively that "it's wrong." But if you know that native English speech also includes the same choice of sound, then when you hear Vietnamese people's English, there is room to take it as "not a matter of accent, but one of the pronunciations that arises naturally from the sound system of their native language."

Knowing just a little Vietnamese also leads to understanding the English that Vietnamese people speak. It is also an opportunity to consider how your own English reaches the other person, in light of how Japanese sounds work.