Verb-Subject Order

Short answer

If the phrase that is being fronted is a Complement of the verb, then it is often best to use Subject-dependent inversion, and if you don't your sentence may sound ungrammatical.

If the fronted element is an Adjunct instead of a Complement, the inversion is not necessary.

It will generally not give good results if the phrase that has been fronted is part of an idiom where it normally follows the verb. For this reason the Original Poster's example is only marginally acceptable at best. The phrase to appear in (a film) has an idiomatic meaning.

Full answer

In the film appear two more girls who think that Dallas is quite rude.

Before we get going we should probably state that the comma after film should not be there, and would be considered "ungrammatical" in this type of inversion.

This example is a bit strange. It doesn't work very well, but this is not necessarily to do with the inversion per se. It's because the preposition phrase in the film is not a proper locative phrase. Secondly, the preposition in belongs with the verb appear. Together these two words have an idiomatic meaning that is slightly different from the sum of their parts (consider A genie appeared in the distance and Di Caprio appeared in Titanic). If you separate them for any reason the idiom doesn't work very well. The following sentences are both not very good:

• *In the film Di Caprio appears.
• *In the film appears Di Caprio.

We can test the same kind of thing with appear and other idioms:

• *Out of sorts De Niro appeared.
• *Out of sorts appeared De Niro.

These are both bad too. What this shows is that we don't seem to be able to move the preposition phrase in the way that we would be able to if this idiomatic meaning wasn't there:

• In the distance, Di Caprio appeared.
• In the doorway appeared a grisly monster.

These examples are both fine. Notice that in the first example there in the distance is an Adjunct (read Adverbial) and a comma is therefore appropriate, but in the second sentence in the doorway is a Locative Complement and no comma is permissible.

Subject-Dependent inversion

Subject-dependent inversion is an information packaging device where the Subject moves to the end of the sentence and the dependent, in this case the Complement, to the beginning.

There are four notable aspects to Subject-dependent inversion. Firstly it is much more common with prepositional phrases than adjectives and it's very infrequent with noun phrases. Inversions with locative preposition phrases are actually quite frequent in everyday speech:

• At the end of the garden is the potting shed.
• There goes the bus.
• Over the road are the chemist's and the Post Office.

Secondly, it usually happens with the verb BE, and rarely with other verbs.

Thirdly, with the verb BE it can only happen with a Complement of the verb , not with an Adjunct (read adverbial). Consider:

• My only friend is in the garden / In the garden is my only friend. (correct)

• My only friend is happy in the garden / In the garden is happy my only friend. (wrong)

Finally, there is a constraint that the Subject contain new information. It can not already have been mentioned in the conversational text so far.

The reasons for using Subject-dependent inversion are usually either that we wish to link the complement with the previous sentence:

• The Police station's at the end of the Road. Opposite the Police station is the ...

Or alternatively, if we haven't mentioned the Subject yet, we may want to make it more prominent by moving it to the end of the sentence, the position that commands the attention of the listener.

• There at the end of the long corridor was the gruesome Flibbertigibbetty

The Original Poster's question

The Original Poster's question involves an attempt by a Spanish writer at such an inversion. It doesn't work well for the reasons given further above. However, the Original Poster's main concern is whether this kind of inversion is obligatory if the locative phrase is fronted.

The answer to this question is that it seems to depend on whether the locative (or other) phrase is a Complement or an Adjunct. Some verbs set up a special space for certain types of phrase. So the verb PUT for example sets up a space for a thing that's being moved and another for the destination of that thing:

• They put [the box] [on the table].

Those two phrases the box and on the table are therefore Complements of the verb PUT.

Now, an Adjunct is an extra phrase that we can stick onto a phrase to give us more information. They are usually preposition phrases or adverbs, but they can also be noun phrases too:

• Bob punched me on Wednesday.

In the phrase above on Wednesday is an Adjunct. It has no special relationship with the verb punch. The verb punch does not set up a special slot for a time that the punching takes place.

Now, if we have a verb like BE which can take a Locative Complement, then if we front the Complement, the sentence will sound very odd if we don't also move the Subject to the end of the clause:

• On the corner is a post-office.
• *On the corner a post-office is. (awkward if not ungrammatical)

However, occasionally we get Subject-dependent inversion with Adjuncts instead of Complements. Here is one with a temporal Adjunct, instead of locative one:

• Seven years later came the great famine.

In cases like this where the fronted phrase is an Adjunct and not the Complement of the verb, the sentence will still sound fine if there is no inversion and the Subject appears in its normal position:

• Seven years later the great famine came.

The first sentence might be considered preferable here because it reveals the Subject dramatically at the end of the sentence. The second example has the rather tame came as the final word. They're both grammatically fine, though.

Notice that we normally expect to be able to move Adjuncts to the beginning of the clause without causing inversion:

• I went to the shops on Wednesday.
• On Wednesday I went to the shops.

No. The sentence

• *In the film, appear two more girls who think that Dallas is quite rude.

is ungrammatical. That's the way German does it, all right, but not English.

Subject-Verb inversion is rare in English; we have Subject-Auxiliary inversion instead.

First, if a verb appears before the subject, it must be an auxiliary verb, not a main verb.
Consequently, appear, which is a main verb, could not be inverted.

Second, Subject-Auxiliary inversion occurs only under very specific circumstances, like questions

• Have you cleaned your room yet?

and also when negative adverbs of time, place, or circumstance are fronted
  (these are negatives that negate the whole clause, so they should be up front)

• Nowhere/Never/At no time/Under no circumstances will he clean his room.

Fronting other adverb phrases doesn't trigger inversion

• In that way/At the party/With no special skill, he will open the champagne.

Even if they're negative, like with no special skill, they don't negate the whole clause.

Third, Subject-Auxiliary inversion is obligatory under these circumstances, even if there is no auxiliary verb in the verb phrase. In that case, Do-Support supplies an auxiliary do to be inverted.

• He cleaned his room yesterday => Did he clean his room yesterday?
• I saw him at no time. => At no time did I see him.

It sounds fine, to me. I think it's from

Two more girls who think that Dallas is quite rude appear in the film.

by, first, preposing the locative:

In the film, two more girls who think that Dallas is quite rude appear.

then Ross's Heavy NP Shift, which moves to the end the heavy NP "two more girls who think that Dallas is quite rude" (see Heavy NP shift):

In the film, appear two more girls who think that Dallas is quite rude.