The oracle curse tongues says, in part, that the oracle that's so cursed must
Pick one of the following languages: Abyssal, Aklo, Aquan, Auran, Celestial, Ignan, Infernal, or Terran.
Whenever you are in combat, you can only speak and understand the selected language. This does not interfere with spellcasting, but it does apply to spells that are language dependent. You gain the selected language as a bonus language.
At 5th level, pick an additional language to speak in combat and add it to your list of known languages.
Emphasis mine. Keep in mind that Ability Scores says
You apply your character's Intelligence modifier to:
- The number of bonus languages your character knows at the start of the game. These are in addition to any starting racial languages and Common. If you have a penalty, you can still read and speak your racial languages unless your Intelligence is lower than 3.
Emphasis mine. What is meant by calling the tongues-cursed oracle's level 1 language a bonus language? Is the language merely added to the list of bonus languages the oracle can pick because of the oracle's high Intelligence score or is the bonus language added to oracle's languages known upon picking the curse?
If the bonus language is added to the oracle's languages known upon picking the curse, why is the addition of another language known at level 5 phrased completely differently, omitting the bonus language concept completely?
To speak in combat from levels 1 through 4 must an oracle pick the language of his tongues curse either as a bonus language due to a high Intelligence score or through the skill Linguistics?
Note: My initial impression was that the bonus language is merely added to the oracle's list of bonus languages that the creature can (but doesn't have to) pick, so an oracle that doesn't pick that language as a bonus language due to high Intelligence could spend levels 1 through 4 not talking at all in combat, but this reading goes unmentioned, for example, by this oracle guide and on the Paizo message boards. I include this information because the initial question did, and some answers address that reading.