Learn German: Januar und Februar sind kalt. - January and February are cold.

Just like in English, we usually don't use a definite article when talking about months in a general sense. However, if you ever do need an article (like saying "the cold January"), remember that all months in German are masculine, so they take der.

How do you pronounce the J in Januar?

In German, the letter J is almost always pronounced like the English Y. So, Januar starts with a Y sound.

Why is the word for cold just kalt and not kalte or kalten?

Because kalt comes after the verb sind (are). In German, adjectives only get extra endings when they come directly in front of a noun (like ein kalter Monat meaning a cold month). When they describe the subject from across the verb, they stay in their basic, unchanged form.

Why do we use sind here instead of ist?

Because the subject is plural. Even though both months are singular on their own, you are talking about two things together (Januar und Februar). Therefore, you must use the plural verb sind (are) instead of the singular ist (is).