In some languages, like Czech or Polish, there should be no single letter words at the end of a line, according to typographical norms. This package handles such situations using LuaTeX’s callback mechanism. In doing this, the package can detect languages used in the text and insert spaces only in parts of the document where languages requiring this feature are used. Another feature of this package is the inclusion of non-breakable space after initials (like in personal names), after or before academic degrees, and between numbers and units. The package supports both plain LuaTeX and LuaLaTeX. BTW: “vlna” is the Czech word for “wave” or “curl” and also denotes the tilde which, in TeX, is used for “unbreakable spaces”.