Ok, this is kind of interesting. [Spoilers for Death Note and ICO]
Let's say Light is, by whatever circumstance you prefer, harmlessly transported to Ico's world, all alone, with the clothes on his back, his watch, his pen, the Death Note, and Ryuk, of course.
Misa is not available to use her Eyes. Ryuk, obviously, finds it way more entertaining if he keeps the information he naturally sees to himself.
Ico has indeed committed a crime. He murdered The Queen. Regardless of the law in his world, that counts for Light.
But that's assuming he even gets to know that much. Light would need proof that he did it, and no one can serve as eye-witness to the crime. …But that doesn't mean it can't be deductively reasoned.
In Death Note, 'Kira' relies on the government to investigate and arrest people. These people, and direct enemies of Kira, are the main targets. So let's say, surrounding civilizations notice that the spooky castle once ruled by the evil shadow queen has sunk into the sea. Perhaps they already know, or soon realize, that the castle's foundations collapsed because of her death. A death that the ritual she was preparing for was specifically arranged to prevent. And there is only one survivor of the incident with the strength to be capable of killing someone.
Would the law enforcement of this world arrest him for murder? Would they be grateful to him for what he did? Would they still fear him for what remains of his horns? It's unclear, but they'd have to at least bring him in for questioning, if found. For the sake of this hypothetical, we'll say that happened. And let's say that's good enough for Light to target him, amongst others.
It probably has to be good enough for Light. He's judging entirely based on what he sees, because every single person around him is speaking a language he does not understand.
Ico's language isn't fully understood even by the fan community. It has similarities to Japanese, which may give Light an advantage in understanding some things, but, that's also why it would be difficult. There are so many natural homophones in a language with simple phonotactic combinations. He'd likely have to learn from a local, entirely from scratch.
Light doesn't like being placed in the role of a child who has to be told what a bear is called via charades. It's one thing to learn a foreign language, like English, as a student in a classroom. It's another thing entirely to be plopped in the middle of a foreign land where you are the weird one for not speaking the same tongue as everyone else.
He's not going to take this slow, either. Frustration will grow, and he will want to be more direct. He may give up on it, he may only learn the word "Name?" (which would be a risky move that could clue someone in to the function of the Note), in either case, he won't get far.
Let's say there's a clearly defined prison house of some kind, and there are records within indicating the names of all the prisoners and those detained for questioning. To accomplish his mission as Kira, he would have to get a good look at each person behind bars, deduce where the names are listed among the many foreign characters written on the records, and, furthermore, associate the right face to the right name when writing it in the Death Note (assuming the records are just descriptions without visual component).
It's an arduous task, especially because he's a complete outsider who can't blend in. Trying to break in to get the records will get him locked up instead. He could try and get a guard's name, and puppet him with the Death Note to get his hands on the records, but that's still incredibly risky given the time it may take him to write the proper names.
The same goes for the paper trick that allows others to see Ryuk. He might try it to scare guards away from their posts. But it could easily backfire if he can't kill those who see the shinagami. Ryuk would get bored if he were forced to keep away from Light, and he is under no obligation to do as Light says.
So if the any of those being spooked away by Ryuk later sees him by Light, then Light runs a real risk of being exiled by these superstitious people. Who would not dismiss a witness to 'evil spirits'.
If you ask me, Light has kind of lost most of his advantages. And if he remains too prideful and impatient to learn the language, he'll never accomplish his ambitions. Assuming he did swallow his pride and develop the patience to become semi-fluent, Ico may already be let out by that time, if questioning was all that was needed. And Light has no grudge against the kid to seek him out. He's going to be pretty safe, all things considered.
