In English, saying "I love you" for the first time is what we say when we fall in love with someone and it shows that we want to build a further relationship. In Chinese and Japanese, "I like you" really means something similar. Does "I like you" in English more or less the same if said to an opposite gender, or just a way to show friendliness?
"I like you" can mean many things. A few of many possible examples I could provide:
I might say to someone, "I like @SEUser." What does that mean? Well, I don't know @SEUser personally, so what I mean to say is "I admire the quality of @SEUser's questions, answers, and comments on ELU SE."
I might be having some work done on my house and say to the service provider, "I like you." Well, again, I don't know the service provider personally, so what I mean to say is "I like the way you do business. You do quality work at a reasonable price. It's a pleasure to work with you."
I might say to a coworker, "I like you." While in this case I do know the other person personally, what I mean to say is "I like the way your brain works. I like your work ethic. We make a good team."
When it comes to more personal relationships, I might say to someone who has attracted my attention (e.g., psychologically or physically), "I like you." What I mean to say is "You appeal to me personally. I'd like to get to know you better. I might like to have a personal relationship with you." In general, my saying "I like you" would not mean "I love you" in the sense that I'd like to spend the rest of my life with you. That said, the relationship could evolve, or not, from one of "I like you" to one of "I love you"; there are no guarantees. "I like you" does not carry the high degree of commitment of "I love you".
"I like you" clearly involves multiple nuances.
Liking someone is not as serious as loving someone. You can really like someone and want to build a further relationship before loving them. At the same time you can fall head over heels in love. Love is more deeper and emotional than "like", in English you usually wouldn't tell some one you love them too soon into a relationship because it is often thought of as an emotion that takes time to develop.
I don't use "I like you" as a statement of intention. For me it simply means I value someone as a person. Sometimes that does mean I want to get to know them better or have a more intimate relationship, but that's an inference you may draw from my attitudes, it's not included in the meaning of my original comment. Another way I commonly use it is to reassure people I view as being socially anxious, who may be worried about whether other people enjoy their company or not. Such people, of course, can be of any gender.
I phrased that all in terms of myself, and my usage, because the truth is that many people – on regional, cultural, or other divisions – use "like" and "love" and all the associated words in different ways, to mean different things. To some extent, this is twofold inevitable:
- the kinds of personal relationships that (say) teenagers and young adults tend to have are different from the kinds of relationships that people in their fifties have, and often each group will re-use the same words in ways that are useful to them in their environment and that they can relate to,
- since personal relationships involve emotional risk, there's often a benefit to using deliberately ambiguous terms, so that you can maintain plausible deniability if your intentions don't play out as you hoped.
Generally it's not reliable to determine someone's romantic intentions by which phrases they use in isolation. Even "I love you" can vary by context, and I have opposite-sex friends to whom I'd feel comfortable saying that, knowing that we've built up sufficient context between us that they'll interpret it as I intend it (unromantically).
Or in other words: if you really want to know how someone feels, you have almost no choice but to just ask them.