The method Romániço uses for this is etymological consensus. The order of preference for new words is:
- A word common to the majority of Romance languages;
- A word common to at least one Romance language and one or more Germanic languages;
- A word in Classical Latin;
- A word unique to only one Romance language.
For example, consider the word sidewalk. The Romance languages each have their own word for it, but most of the Germanic languages (and Russian) borrow their word from the French, which makes trottoir the most widely recognizable choice.
Once a candidate is arrived at, the immediate Latin source — or whatever phonetically spelled form of the word is available, in the case of non-Latinate words — is determined. In the case of Latin sources, recast nouns in the genitive* stem and add -o (or -uo to those with a genitive ending in -us, where necessary to prevent homynms); recast simple verbs in the present tense stem, affixed verbs in past participial stem, and add -er; indicate irregular stress, if any, with acute accents. In the case of trottoir, which is part Frankish and part Latin, it may be broken down to medieval Latin trottare (“to go”, from Frankish *trotton “to run”) + -oir, which comes from classical Latin -ōrium, yielding trottorio.
Be mindful of homonyms — both at the root level and with affixes — and be prepared to find or fudge alternate forms of a word to avoid conflict with other words. For example, Latin portare (“to carry”) became Romániço porter, so portus (“port”, genitive portūs) became portuo and porta (“door”) became portelo.
Then apply Romániço’s orthography: Change q to c, hard c to ch before e and i, soft c to ç at the end of a noun or adjective root; keep final -que as -che (not -cue); hard g to gh before e and i, soft g to ģ at the end of a root; sce-, sci- to ce-, ci-; -nct- to -nt-; ph to f; vocalic y to i; double letters to single. Reduce agentive -arius to -aro. Trottorio thus becomes trotorio, and Romániço at last gets its word for sidewalk.