"für dich" or "dir"?

Question

Would you say, for example,

Bin ich dir zu laut?

or

Bin ich zu laut für dich?

Relatedly, how do you know to use accusive vs. dative when it English it´s unclear such as 'That´s too late for me`.

Answer 1

Bin ich dir zu laut? (preferred)

Bin ich zu laut für dich?

These are both okay. The first variant uses a dative object, the second a prepositional object with a preposition which needs the accusative —it's not an accusative object!

That's too late for me.

Das ist mir zu spät. (preferred)

Das ist zu spät für mich.

Again, both variants are okay. The one with dative object is snappier. Most German speakers would mumble D'ismir z'spät.

Answer 2

I am not satisfied with the accepted answer. Although it is right for most of the cases, you can not say that one option is preferred without specifying the context.

Choosing dative or für practically always has implications. We will start from what is probably the commonest dative. Then we will analyse the type of dative we have here (dativus iudicantis). Lastly, I will demonstrate how the choice alters the meaning in the original sentence. If the following is too long for you, please jump to the last section.

Commonest Dative vs für

Für mich/dich generally places more emphasis on the beneficiary. Dative tends to denote a recipient/sufferer/judge. This is very hard to generalise. Please note the examples below.

Das gebe ich dir für Vater/This I give you for father.

Similarly you can say

Ich stahl dir Geld./I stole money from you (in a very marginal case it could mean for you).

The dative here is called dativus incommodi, because it denotes the person incommoded/inconvenienced.

But

Ich stahl für dich!/I became a thief for you!

Judging Dative vs für

Concerning examples of the precise type in question there is a very important difference

Das ist ihm zu kompliziert./That’s too complicated for him.

always denotes a perception of the described person himself! This dative is called dativus iudicantis, because it describes who is judging.

Das ist zu schwer für ihn./That’s too heavy/difficult for him.

can be someone else’s opinion! Typically the describing person’s opinion.

Thus you can have:

Das ist mir für ihn zu schade!/I deem this as too precious for bestowing it on him!

The most impressive example might be:

Sie ist Millionärin, aber das Auto ist ihr zu teuer./She is a millionaire, but deems the car too expensive.

On the other hand:

Ich bin kein Millionär! Das ist zu teuer für mich!/I am no millionaire! I can’t afford that!

An important subclass is the impersonal objective judgement:

Die Dosis war zu hoch für ihn und er starb./The dose was too high for him and he passed away.

The asker’s concrete sentence

In the concrete example given, we will, in accordance with the above, say:

Bin ich dir zu laut?

only if we want to inquire about the asked person‘s own noise limits. By contrast

Bin ich zu laut für dich?

could be a less preferred version of the same (as the accepted answer shows) but more importantly is the only option, when the asked person and the judging person do not coincide. Let’s say we have a hyperacustic man marrying a very noisy lady with a penchant for death metal. She could ask:

Warum ist deine Mutter gegen unsere Heirat? Bin ich zu laut für Dich?/Why does your mother oppose our marriage? Am I too loud for you?

You can even add the aforementioned dativus iudicantis to show this is mother’s judgment:

Warum ist deine Mutter gegen unsere Heirat? Bin ich ihr zu laut für Dich?

Analogously, a doctor will say:

Es ist zu laut für den Patienten.

while

Es ist dem Patienten zu laut.

reports the patient‘s own judgment.

Special cases

We only say:

ist das ein Problem für dich?/stellt das ein Problem für dich da?

We never replace this with dative. English usage probably played a role here. According to the observation of three generations of my family (seconded by ngram) between 1950 and 2000 there has been an enormous rise in the frequency of „wir haben ein Problem“ and similar phrases. We tentatively attribute this to Hollywood.