The schwa is the sound of the atonic vowel (in the syllables not accented) very weakly pronounced. This sound is extraneous to Italian, to the Tuscan, to the Spanish, to the Latin, to the Greek, while it is existing in the Germanic languages (German, English, etc...), in French, in Romanian, Arab, etc... so we can say that majority of languages and dialects in the world use the schwa. In the international phonetic alphabet this sound is represented by an upside-down e.

The schwa in English can be represented for example, by any vowel or group of vowels. As we know, English has a strong divergence between alphabetical system and pronunciation.

the a of along
the e of robber
the i of incredible
the second o of bottom
the second u of thesaurus

We take for ex. some French verses of Arthur Rimbaud and we marked in boldfaced the schwa.

Fêtes de la faim

Si j'ai du got, ce n'est gures
Que pour la terre et les pierres
Dinn ! dinn ! dinn ! dinn ! je pais l'air,
Le roc, les Terres, le fer.

Tournez, les faims ! paissez, faims,
Le pr des sons !
L'aimable et vibrant venin
Des liserons ; [...]

It is a phonetic System certainly easier than English.

In German the schwa is found in infinitive verbs (essen, kommen, bitten, etc ...), in the final e of  words Name, bollards, heute, etc...

In the Sanmartinese dialect the sound schwa is the vowel used more richly. We take an any sentence, marking the schwa in boldfaced (correspondent always to one e).

1) - Ujje sienghe jute fore, ma prime fatte 'na mmasciate.
2) - Chi ne t fijje, nen ce j n parre n pe' quesijje.