**Jos kirjoitus- ja äänneasu päättyvät konsonanttiin, käytetään perusmuodon ja päätteen välissä sidevokaalina i:tä, esim. Caracas : Caracasissa** looks most closely as a rule & solution to this potentially eternal problem of your name taken from http://www.cs.tut.fi/~jkorpela/kielenopas/all.html#vier-taiv. Korpela himself has written various online manuals & guides of various subjects over the years. http://www.cs.tut.fi/~jkorpela/Finnish.html
What that text says is shortly that if written & spoken form of a foreign word ends with a consonant 'i' is the vowel to be used between the base & suffix.
With the original problem regarding who's the Caracas case would be 'Caracasin' not 'Caracaksen' or if there was something in you it'd be 'Takhisisissa' - still wanna learn our lingo ?
What that text says is shortly that if written & spoken form of a foreign word ends with a consonant 'i' is the vowel to be used between the base & suffix.
With the original problem regarding who's the Caracas case would be 'Caracasin' not 'Caracaksen' or if there was something in you it'd be 'Takhisisissa' - still wanna learn our lingo ?