I took a trip down to Mexico last week and I heard "so-so" in response to "Do you speak English?" Now, I'm used to hearing "so-so" more in the context of "all right" or "OK", but not as in "more or less". Is this usage correct or is it a lack of good teaching?
According to Merriam-Webster, "so-so" means "neither very good nor very bad."
According to The American Heritage Dictionary, "more or less" is an idiom meaning "basically, essentially."
I have often heard Japanese and Korean students of English also use "so-so" in terms of their English proficiencies, and based on cultural context (outward humility), I think they mean to say that they are okay at English, but not great, rather than the seemingly less humble meaning of "more or less" (saying they can basically speak the language).
So-so means "passable".
When you ask 'Do you speak English?', the response means that though the speaker has the ability to speak English, he might have difficulty in finding grammatically and situationally apt words or phrases or pronunciations in his speech because he is accustomed to a local English dialect which is different from the dialect and accent used by the questioner.
In other words, he is "more or less" able to convey the intended meaning depending on the mutual understanding of the respective local English dialect.
Similarly, when you say your food is so-so, you mean that it is "more or less" okay to eat, depending on your own perspective. For example, one might not find anything excellent about a particular dish, but the spice level might tinge his tongue more than someone who might find the same dish a little bland, but not sufficing enough to complain.
It's probably meant in the context of "my English is so-so". That would fit the "alright or OK" definition you mention.
The problem is that in Spanish "más o menos" means both "more or less" and "so-so". As a result people are often confused about which one to use in English. In the same way that English speakers get confused about using "ser" or "estar" in Spanish. The response "more or less" to the question "Do you speak English?" or "How is your English?" isn't really correct but an English speaker will understand the idea!
When I was in USA I got a book which has a table indicating grades of quality, something as following:
excellent, good, fair, so-so, very poor (This case it means the opposite of good: 'not good').
Another day I asked an American friend the meaning of so-so. He told me that is close to "more or less" but something that is not good.
For example, if you do some work and ask you customer about it and you get "SO-SO" this means that your work is passable but don't have the expected quality.
If the question was, how is your English? then So-so would be an appropriate response. To the question, do you speak English? it is incorrect.
I personally hate the use of so-so when people give a judgement about something. When students are learning English, so-so is a lazy response that they over use in many countries rather than challenge themselves with the wide range of adjectives they could use. As a teacher in China I do not allow my students to use it in class and encourage them to use one of a hundred other possible responses.
As far as I know, "more or less" relates to quantities. For example, "She has more or less 500 books at home". I believe it's similar to "She has 500 books or so at home" and "She has about/approximately 500 books at home". On the other hand, when a question is asked with "how", we might answer it saying "so-so". "A: How was your day today? B: It was so-so".