Can I help you?

[Wanwo]

Can I help you?

わたしわたすけてもいいか?

I want to use this phrase for speaking to a stranger in public in a friendly way. Is my translation any good? Is there a more natural way to say it?

[NickT]

助ける usually means help more as in "help! I'm in danger!" than "do you need a hand with something?". I would be inclined to use 手伝う instead.

I would also drop the わたし as it is not really required.　

How about these:

手伝いましょうか - Shall I help you?
手伝わせてください - Please allow me to help you (perhaps too formal?)

Or perhaps:

助けは要りますか - Do you need assistance? (sounds like something a shopkeeper might say)

I'm not totally sure I understand what context you would use this in. Is it when someone obviously needs some help? E.g, if they are struggling with heavy bags, or they look lost? Or is it just an opening gambit to start a conversation, with someone who probably doesn't require any help?

[Wanwo]

Yes, I think you're right. I mean help as in lending a helping hand. Help not necessarily required but offered out of friendliness.

手伝いましょうか may be the right phrase.

What does ましょう mean?

Could I just say 手伝い (with rising intonation)?

[Jason]

手伝いましょうか is what you're looking for.

What does ましょう mean?

ましょう is the polite volitional verb ending. When used in a question, it's roughly equivalent to "shall I...?" You get it by chopping the す off of a ます form verb and replacing it with しょう.

Could I just say 手伝い (with rising intonation)?

No. Well, I suppose you could, but it would sound rather uneducated. It would be like someone coming up to you to offer help and saying "Help?"

手伝わせてください - Please allow me to help you (perhaps too formal?)

For someone you just met on the street and just offering to help them with their bags (or some similar situation), this is much too forward. This is more appropriate for people you know. *In terms of assertiveness, ください is considerably more forceful than ましょうか.