Grammatically Correct: The writer's essential guide to punctuation ...

GRAMMATICALLY CORRECT
"You said it had to be descriptive. What the hell's the difference if
it's about a baseball glove?"
-J.D. SALINGER, The Catcher in the Rye
In fiction writing, some authors use italics to represent words
that are being thought by a character, rather than spoken aloud.
This is permissible, but not really necessary: Leaving off quotation
marks should be sufficient to indicate your intentions (although you
must be careful to distinguish these words in some way from the
narrative). Because of the other purposes served by italics, using
them to indicate unspoken words may appear to give those words
an unintended vehemence or significance.
Another use of italics in fiction is for the text of a note or letter
that a character is reading or composing: Writing within writing, as
it were.
SETTING OFF NON-ENGLISH WORDS
Words from other languages are set off in italics as a signal that
they should not be processed the same way as the rest of the text.
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Here are a few French terms for fans at the Forum:
Batail/e, Escarmouche, Bagarre generale-The three stages of mind­
less hockey violence. A bataille is generally waged by two players with
no outside interference. When a third party joins the fracas, it escalates
into an escarmouche. This is often the signal for every player on the
ice to drop his gloves and go at it; the ensuing obscene spectacle is
your basic Pier Six bagarre genera/e.
-MICHAEL FARBER AND MIKE BooNE, in The Anglo Guide to
Survival in Quebec
'Oh, look!' broke in Gherkins. 'Here's a picture of a man being
chopped up in little bits. What does it say about it?'
'I thought you could read Latin.'
'Well, but it's all full of sort of pothooks. What do they mean?'
'They're just contractions,' said Lord Peter patiently. ' "Solent quoque
hujus insulae cultores"-it is the custom of the dwellers in this
island, when they see their parents stricken in years and of no further