No, it is not only a Slavic custom - amongst the Catholics the Melkites and Romanian Greek Catholics also have this tradition.
In most places even though it is a Matins service it is “anticipated” on Wednesday evening rather than Thursday morming. Several versions of the
Typikon call for it to begin at the fourth hour of night or about 10 p.m.; this is generally only followed in monasteries and most parishes have it earlier in the evening.
Traditionally the life of St. Mary of Egypt is read during the service; it can be read online at
orthodox.net/saints/mary-of-egypt.html
Holy Trinity Monastery (Jordanville) has printed a very nice book containing not only the entire Canon, but the life of St. Mary of Egypt and the subdivisions of the Canon for the first four days of Clean Week. The divisions of the Great Canon for the first week can be found at
orthodox.net/greatlent/index.html
Getting back to more general Lenten practices, on Friday evenings as bpbasilphx has pointed out, some Melkite parishes celebrate Small Compline with the Akathist Canon and portions of the Akathist Hymn to the Mother of God broken up into four divisions; on Friday of the Fifth Week (the vigil of Akathistos Saturday) the entire Akathist is chanted. This is a Greek tradition and is generally not followed in Ukrainian or Russian parishes.
The Akathist to the Passion of Christ is prayed in some Ukrainian Catholic and Orthodox parishes on Friday evenings where either Presanctified is not offered or is offered on Friday morning. The Akathist to the Mother of God is generally only taken once during Great Lent on Akathistos Saturday (or the evening before) in the Ukrainian tradition.