Brithenig, or also known as Comroig,^[2] is an invented language, or constructed language ("conlang"). It was created as a hobby in 1996 by Andrew Smith from New Zealand, who also invented the alternate history of Ill Bethisad to "explain" it. Officially according to the Ill Bethisad Wiki, Brithenig is classified as a Britanno-Romance language, along with other Romance languages that displaced Celtic.^[3]

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Brithenig was not developed to be used in the real world, like Esperanto or Interlingua, or to provide detail to a work of fiction, like Klingon from the Star Trek franchise. Rather, Brithenig started as a thought experiment to create a Romance language that might have evolved if Latin had displaced the native Celtic language as the spoken language of the people in Great Britain.

The result is an artificial sister language to French, Catalan, Spanish, Portuguese, Romanian, Occitan and Italian which differs from them by having sound-changes similar to those that affected Welsh, and words that are borrowed from the Brittonic languages and from English throughout its pseudo-history. One important distinction between Brithenig and Welsh is that Welsh is P-Celtic, but Latin was a Q-Italic language (as opposed to P-Italic, like Oscan), and the trait was passed onto Brithenig.

Similar efforts to extrapolate Romance languages are Breathanach (influenced by the other branch of Celtic), Judajca (influenced by Hebrew), Þrjótrunn (a non-Ill Bethisad language influenced by Icelandic), Venedic (influenced by Polish), and Xliponian (which experienced a Grimm's law-like sound shift). It has also inspired Wessisc, a hypothetical Germanic language influenced by contact with Old Celtic.

Brithenig was granted the code BZT as part of ISO 639-3.

Andrew Smith was one of the conlangers featured in the exhibit "Esperanto, Elvish, and Beyond: The World of Constructed Languages" displayed at the Cleveland Public Library from May through August 2008.^[4] Smith's creation of Brithenig was cited as the reason for his inclusion in the exhibit (which also included the Babel Text^[5] in Smith's language).

This section does not cite any sources. (February 2023)

Brithenig orthography is similar to that of Welsh, except:

• Unlike Welsh, Brithenig has soft C and G; that is, before vowels e and i the consonants c and g are pronounced /tʃ/, /dʒ/, similar to Italian.
  • Brithenig also use such phonemes finally in letters c' and g'.
  • Hard G in Brithenig is indicated by gh as in Italian.
  • Similarly, when preceding e and i, sc is pronounced /ʃ/, otherwise /sk/.
• The letter k used for hard /k/ is much more alive in Brithenig than Welsh.
• While Welsh words are usually stressed in penultimate syllables, Brithenig words are stressed in the last syllable (Brithenig yscol vs. Welsh ysgol, both mean "school").
• There are no complicated rules on predicting vowel length from orthography: stressed vowels are always pronounced long.
• Brithenig has numerous silent letters.
  • In words more than two syllables, word-final -t in the sequence -nt, and -r or -l as the second members of consonant clusters become silent.
  • Word-final -f generally silent, but not as an orthographically geminate -ff.
  • In the infinitive endings -ar, -er, -ir, the -r is usually unpronounced.
• Some speakers pronounce -ae and -oe as /aː/ and /oː/, respectively. In the standard variant, both vowels are pronounced as /aːɪ/ and /oːɪ/.
• Monosyllabic words ending in consonant clusters which ends in -r or -l are pronounced with an epenthetic vowel same as the last vowel (llifr pronounced as llifir /ˈɬiːvɪɾ/, see above). Such would account for unusual stress patterns.

Most of Brithenig's vocabulary is distinctively Romance even though it is disguised as Welsh. This list of 30 words gives an impression of what Brithenig looks like in comparison to nine other Romance languages, including Wenedyk, and to Welsh. The similarity of about one quarter of the Welsh words to Brithenig words (indicated by not being bracketed) is because of their common Indo-European background, but a few others, such as ysgol, were borrowings from Latin into Welsh.

The Lord's Prayer:

Nustr Padr, ke sia i llo gel:
sia senghid tew nôn:
gwein tew rheon:
sia ffaeth tew wolont,
syrs lla der sig i llo gel.
Dun nustr pan diwrnal a nu h-eidd;
e pharddun llo nustr phechad a nu,
si nu pharddunan llo nustr phechadur.
E ngheidd rhen di nu in ill temp di drial,
mai llifr nu di'll mal.
Per ill rheon, ill cofaeth e lla leir es ill tew,
per segl e segl. Amen.

• British Latin