Learn Spanish (Spain): Los estudiantes hablan inglés y español.

The sentence is using the regular -ar verb hablar (to speak). Because the subject is los estudiantes (they), we drop the -ar and add the "they" ending, which is -an.

Is estudiantes masculine or feminine?

The singular word estudiante ends in -e, so it is used for both! You rely on the article to show who you mean: el estudiante (male) or la estudiante (female). Here, the masculine plural los is used, meaning this is either a group of male students or a mixed group of males and females.

Why aren't the languages inglés and español capitalized?

Unlike in English, Spanish languages and nationalities are written in lowercase unless they are the very first word of a sentence.

Why is there an accent mark on inglés?

Words ending in -n, -s, or a vowel naturally put the spoken stress on the second-to-last syllable. Since we need to emphasize the final syllable for this word (in-GLES), we have to write an accent mark to break the normal rule.