What language does Worf speak on a daily basis?

Question

Worf obviously knows Klingon as he has been seen translating Klingon phrases for his Federation colleagues.

Gowron: We shall see. (in Klingon) CHEGH-chew jaj-VAM jaj-KAK!

Worf: He said, "Today is a good day to die."

_{DS9: The Way of the Warrior}

But having been mostly raised by humans, he would be proficient in English as well (or Russian possibly... but an Earth language nonetheless).

So, what language does Worf regularly use throughout the shows? Does he speak Klingon and let the Universal Translators do their job or does he speak English, switching it up while in Klingon company?

Why this question is interesting:

Klingons tend to look down on Worf for "abandoning" his Klingon heritage in favor of Federation ideals. Despite his efforts to be as Klingon as possible, he's still an outcast among his people. If Klingon isn't his native language and he speaks it with an accent or speaks in English instead, it gives Klingons another reason to think of Worf as an outsider no matter how many times he proves his honor in other ways.

EDIT:

I'm aware of the inconsistencies in the way the universal translators decide to translate, especially when dealing with the Klingon language (which is what makes this question so hard for me to figure out on my own). What I'm looking for is something in the dialogue or some other sort of reference that indicates what language he's using. Perhaps a Klingon who pokes fun at Worf's accent/improper use of the Klingon language or looking down on him for spending most of his time speaking like a human. Something like that.

Answer 1

(From my comment on my previous answer) It would be impossible to tell. It is believed that the Universal Translator can fit in a Starfleet officer’s Combadge. If this is true, then unless you find Worf tapping it (or somehow interacting with it), when actually speaking Klingon (sometimes he speaks Klingon and we hear it), Worf may be capable of speaking English without a Universal Translator. Also, you made a mistake because when he speaks to Klingons, he often speaks in Klingon and English. Also, Worf lost his parents in 2346 (when he was 6 years old) when the Romulans attacked the Khitomer colony. Worf grew up in a Klingon society for six years of his childhood until he became part of a human society (in which he got his foster parents). However, Worf is still a native Klingon and I would expect that he would be capable of speaking Klingon, just as he is capable following all the traditions and customs of Klingons.

However, in season 1, episode 19 (Heart of Glory), three Klingon fugitives come aboard the Enterprise, they speak to Worf about how for a Klingon to serve on a human Starfleet vessel. Worf tells the computer “O’mat gri t’m pffiots” (a type of Klingon food), with no noticeable objection from the Konmel and Korris. This makes me believe that Worf speaks Klingon and English both fluently. Notice that whenever a Klingon ship is seen and its crew communicates to the Enterprise’s bridge they always speak in English, because they are capable of it; in season 2, episode 8 (“A Matter of Honor”), Riker comes aboard a Klingon vessel as a participant of the “Officer Exchange Program”. At some point when Riker takes the oath to obey Captain Kargan’s orders, Lieutenant Klag objects and tells Kargan that Riker is lying in Klingon; Captain Kargan tells Lieutenant Klag also in Klingon to “Speak in their language!” I am not sure why the Klingon fugitives aboard the Enterprise in “Heart of Glory” do not prefer to speak Klingon with Worf. This post may be an explanation as to why the Klingons prefer to speak to Worf in English, however it still comes back to the idea that they are using a Universal Translator. I could not find any episode in which a Klingon accuses Worf of not being able to speak Klingon well. Konmel specifically says, “Tell me, what is it like for the hunter to lie down with the prey”. Korris says, “Does it make you gentle”. The fugitives believe that Worf is like them, that humans have been forcing him to act with kindness. Worf says, “Yes... yes, those feelings are still a part of me. But I control them. They do not rule me” At about the end of the episode, Korris says to Worf, “You are a sham. My words were dust upon the ground. Your blood has no fire. You are weak like them. I don’t care what you look like—you are no Klingon!” Worf is found as an outcast in other perspectives from Klingons, but I believe not because of the way he speaks.