speak with someone <in order> to…

[dwni]

Hello! I have looked the verb ‘speak’ up in a dictionary.
According to the dictionary the structure of speak is ‘speak to somebody about something’.
For example, I am at the local shop trying to buy some fish. In order to do this, I ask someone to tell me where the fish is.
Can that person say
1Speak to the shop keeper to get some fish.
2 Speak to the shop keeper in order to get some fish.
Are the sentences okay? Can speak be used without ‘about’ and with to/in order to for purpose?

 

[lingobingo]

No, your examples aren’t very natural. The expression is “speak to someone about something”, but I’d hesitate to call it an idiom or set phrase. It’s just one use of the verb to speak.

I have a complaint.​

You’ll have to speak to the manager about that. I’ll see if I can find her.​

 

[dojibear]

I ask someone to tell me where the fish is.
Can that person say
1 Speak to the shop keeper to get some fish.
2 Speak to the shop keeper in order to get some fish.
Are the sentences okay? Can speak be used without ‘about’ and with to/in order to for purpose?

In my dialect of AE, these imperative (command) sentences sound okay.
But they are only okay if they express the meaning you want to express:

In order to get some fish, you must talk to the shop keeper. Tell them what fish you want, and they will get the fish for you.

 

[dwni]

what about
1 In order to get some fish, speak to the shopkeeper.
2 In order to get some fish, speak to the shopkeeper about it.

 

[lingobingo]

They’re grammatically correct, but extremely unlikely things to say. It’s hard to imagine any normal situation in which that might be said.

To speak to someone about something is usually used in the sense of consulting them about a certain matter, or reporting something to them.