Translation:It is far too difficult to decide.
It's a part of the verb. "Han bestemmer seg" would literally translate to "He decides himself" in English, but while this is the wrong way to say it in English, this is the correct way to say it in Norwegian.
Just remember that seg' might change depending on the subject: "Jeg bestemmer meg for å fiske." = "I decide to go fishing."
If I understand correctly; would the use of "seg" (without a pronoun preceding it such as han or hun) equate to talking about oneself in the third-person or in a way that doesn't explicitly refer to one's self as the subject? Just in the same way that in English you don't constantly refer to yourself explicitly in every single sentence that talks about actions or thoughts that you (yourself) are doing or thinking.
If the above is true, would the sentence translate as: "It is far too difficult for one to decide"? If one were to be literal about it.
I must stress that a word for word translation is not what I'm looking, rather the concept that it is expressing.
I would say, not quite. You normally use this phrasing when you want to talk generally, and not imply any person. It could maybe be used in the way you describe, but it could equally be used when talking about the person you are talking to. For instance "Jeg forstår det er vanskelig å bestemme seg, men du har ikke mye tid igjen nå", meaning "I understand that it is difficult to decide, but you don't have much time left now". Here you refer to the person you are talking to with the "seg" pronoun.
But it is important to remember that there are only a limited number of verbs that can be used with such a pattern, allbeit not that limited. It's actually relatively common. "Å bestemme seg/meg/deg" is a phrasal verb meaning "to make up ...'s mind". Other verbs that use the same pattern are for example "å skjære seg", "å skynde seg", å "glemme seg", "å prøve seg", and quite a number of others.