I see this in a lot of translated quotes, but i don't understand why. the quote in it's original language wouldn't have implied accept but only put [ac]cept and the translator wouldn't be so poor a speller to have forgotten the h in t[h]is.i get the point of the bracket insert when it needs to say something like [consequentlly] .
In general, the square brackets indicate the the person who is citing has changed the original quote. One is only supposed to do this if it improves the flow of your writing, so long as it doesn't change the meaning of the original quote. You can change the tense of words, or add words if the part you are quoting is missing an important detail for the reader's understanding, like a name. For example, say my original quote is this, Timmy liked to play baseball. You might be writing a literay essay, which should always be in the present tense. So you might say Timmy is an athletic child, who like[s] to play baseball. You can manipulate the quote to make the tense work with the rest of your sentence, so long as the information is the same. You may also want a quote from a source that names someone, but uses a pronoun in the particular part you want to quote. To make it easy for your reader to know who you are talking about, you can add a clarifying word or name.
