Formal vs. conversational

VerbGeneral ideaWhen to use
SPEAK More formal, often one-directional. (doesn't need a receptor) Languages, ability, addressing a group, formal situations.
TALK More informal, conversational. It needs a receptor A two-way exchange of ideas with someone.
They often overlap: "Can I speak to you?" and "Can I talk to you?" are both correct and mean almost the same thing. But some collocations are fixed and NOT interchangeable: "speak English" (never "talk English"), "small talk" (never "small speak").

Common patterns & fixed expressions

SPEAKTALK
speak a languagetalk about something
speak uptalk to / with someone
speak your mindsmall talk
speak in publictalk business
speak fluentlytalk nonsense
generally speakinghave a talk (noun)
Examples in sentences:
She speaks three languages.
We talked about the weekend.
Could I speak to the manager, please?
Stop making small talk and get to the point.

Speak/Talk WITH vs. Speak/Talk TO

Both prepositions introduce the other person in the conversation, and in most everyday situations they're interchangeable. But there's a subtle difference in feel.

PrepositionFeelTypical use
WITH Mutual, two-way — both people take part equally. More common in American English. Emphasizes "together".
TO The neutral, most common choice overall. Can sound more one-directional or serious with "speak" — one person addressing the other.
Examples:
I talked with my sister about our plans. (mutual conversation)
I talked to my sister about our plans. (same meaning, very common, neutral)
The manager needs to speak to you. (serious, one-directional feel)
We spoke with the neighbours and solved the problem together. (collaborative)
Don't overthink it: In everyday conversation, "Can I speak/talk to you?" and "Can I speak/talk with you?" are both completely natural and mean almost the same thing. The WITH/TO difference is a subtle style choice, not a grammar rule you can break.

Exercises

Speak or talk? Type the correct verb.

1.She __ perfect English.
2.Let's __ about your weekend.
3.Can I __ to you for a minute?

4. "She doesn't ___ Spanish very well."

5. "We stayed up all night just ___ nonsense."