dialekto

What a dialect is. A dialekto is a variety of a language marked by region or group, differing in pronunciation, vocabulary and sometimes grammar, but still the same language: Bavarian and Low German are dialektoj of German. Where the differences are large enough that speakers cannot understand one another, you have separate lingvoj, and the line between the two is political as often as it is linguistic.

"Esperanto has no dialects" is half true, and the false half is more interesting. There are no regional dialects, and that is a genuine achievement: an Esperantist from Brazil and one from Japan write the same language, because there is no territory for a variety to grow in and no monolingual community to grow it. But varieties do exist, and pretending otherwise does learners no favours.

Where the variation actually lives. National accents are real and audible; a French speaker's r and a Japanese speaker's vowels are not the same, which is what the notes on spoken Esperanto are for. Vocabulary drifts by generation and by circle, and the youth movement has a slang the congress hall does not use. There is a long-running stylistic split between conservative Zamenhofan writing and a looser modern register, and a parallel one between people who reach for a compound built from existing roots and people who reach for a new international loan. What keeps all of it inside one language is the settlement described in the notes on the Fundamento and the Academy: a fixed core that nobody may revise, and free growth around it.

The words for talking about it. Dialekta is dialectal, dialektologio is dialectology, akĉento is the accent, idiomo an idiom or an established way of putting things, and dialekto should not be confused with dialektiko, dialectic, which is an unrelated word from the same Greek root and a different argument entirely.