Strangely, I don't notice non-native speakers of English making spelling errors all that often.
Instead I notice them making the same grammatical errors over and over again. For instance Chinese speakers frequently mangle English plurals and omit articles "a" and "the".
So I think the hardest part of learning any language is always the grammar rather than the words, if the grammar differs from your native grammar. It's easy to map "aeroplane" to "avion" but much harder to map "the" to "le/la/l'/les/las" depending on context.
I think the hardest part of learning any language is always the grammar rather than the words, if the grammar differs from your native grammar.
That fits my experience as a foreign-language teacher (Chinese to native speakers of English, English to native speakers of various Sinitic languages and to speakers of Japanese, Biblical Hebrew in the medium of Modern Standard Chinese to Taiwanese persons of varying native languages, including one non-Sinitic native language). The categories that are hardest to notice in the acquired language are the categories that don't even exist in the speaker's native language. (For example, Chinese has neither number for nouns nor tense for verbs, nor does it have indefinite or definite articles, so native speakers of Chinese regularly confuse those issues in English.) This is especially so when the grammatical features are marked by phonological features that don't exist in the first language. Chinese does not have syllable-final consonant clusters, so a Chinese speaker's ear is not practiced in hearing those in other languages. So the difference between "fix" (present tense) and "fixed" past tense can be missed on TWO levels by a native speaker of Chinese learning English, as can the difference between "sixth" (singular) and "sixths" (plural).
Americans, of course, make a huge number of grammar mistakes when speaking Chinese, and rarely notice themselves doing so.
Instead I notice them making the same grammatical errors over and over again. For instance Chinese speakers frequently mangle English plurals and omit articles "a" and "the".
So I think the hardest part of learning any language is always the grammar rather than the words, if the grammar differs from your native grammar. It's easy to map "aeroplane" to "avion" but much harder to map "the" to "le/la/l'/les/las" depending on context.