While they were at breakfast, the letters were brought in. (Austen)
I have finished breakfast, ring the bell. (Ch. Bronte)
The definite article is used when the nouns are modified by a particularizing attribute or when the situation makes them definite.
Thedinner we had to-day was very substantial.
Thedinner was a success.
The indefinite article is used if the name of a meal is modified by a descriptive attribute.
After ahearty breakfast the four gentlemen sallied forth to walk to Gravesend.
(Dickens)
The use of articles with names of languages.
Names of languages when they are not followed by the noun language are used without articles:
She knows English.
Note the peculiar use of the definite article in: (1) It is a translation from theEnglish (the French etc.), (2) What is theEnglish (the French etc.) for ‘сосна’?
The definite article is used if the noun is modified by a particularizing attribute:
The English of America differs from the English of England.
When the noun language is mentioned the definite article is used: the English language, theGerman language.