Overview
The borders of the Belgian Sprachraum are made up by the Canche and the Authie in the south-west, the Weser and the Aller in the east, and the Ardennes and the German Mittelgebirge in the south-east. Some scholars associate it with the Nordwestblock, more specifically with the Hilversum culture.
The use of the name Belgian for the language is to some extent supported by Julius Caesar's De Bello Gallico. Some terms can be traced directly to Celtic, such as Indutiomaros (Gaulish maros 'great', 'powerful'), Eburovices (similar to Eburacum, York) or Boduognatos (compare the Irish mythological figure Bodb Derg)
Caesar mentions that the Belgae and the Galli spoke different languages, which is partially supported by toponyms in present-day Belgium, which, according to Kuhn, point at the existence of an Indo-European language, distinct from Celtic and Germanic languages.[4] Hans Kuhn also noted certain connections (suffixes, ethnonyms, toponyms, anthroponyms) between this language and the Indo-European languages of southern Europe, in particular with the Italic languages. Before their migration to the south, the Italics might have resided in central Europe, in the vicinity of the Germans, Celts and the Slavs, as shown by the amount of vocabulary common to these groups. Some of them may have migrated to the northwest, while the others headed for the Italian peninsula.[1][2]
Proponents of the Belgian language hypothesis also suggest that it was influenced by Germanic languages during a first, early Germanicisation in the 3rd century BC, distinct from the Frankish colonization in the 5th to the 8th centuries AD. For example, the Germanic sound shifts (p → f, t → th, k → h, ŏ → ă) have affected toponyms that supposedly have a Belgian-language origin.
Characteristics of Belgian are said to include the retention of p after the sound shifts, a trait that it shared with the Lusitanian language. Names of bodies of water ending in -ara, as in the name for the Dender; -ănā or -ŏnā, as in Matrŏnā (Marne River and also the current Mater) and settlement names ending in -iŏm are supposedly typically Belgian as well.
According to Gysseling, traces of Belgian are still visible. The diminutive suffix -ika, the feminizing suffixes -agjōn and -astrjō and the collective suffix -itja have been incorporated in Dutch, sometimes very productively. In toponymy, apa, poel, broek, gaver, drecht, laar and ham are retained as Belgian loanwords.