Same movie but with different names

Setting aside working titles and translated titles, there are other reasons why a movie might be released under an alternative title. In the case of Unleashed vs. Danny the Dog, one of the reasons appears to have been heavy editing/censorship:

Already when the movie has been shown in European cinemas, some magazines wrote that the European version was different in some points from the U.S. version. This apparently affected all countries where the movie hadn't been released with the title "Unleashed", but with the title "Danny the Dog". These countries weren't just European, but also states like Hong Kong. The versions can be kept apart right at the beginning because of different titles (except in the U.S., where both versions are called "Unleashed" but differ as "unrated" and "R-rated").

A better example of a movie which was released under an alternative title for similar reasons is Dario Argento's Phenomena which was released in the US as Creepers. The American version is shorter than the original by 30 minutes.

Title changes are sometimes made because the original title might not be understood in a particular market. A famous example is Harold and Kumar go to White Castle which, in the UK, was released as Harold and Kumar get the munchies as the restaurant chain does not have a presence there.

Some alternative titles are chosen simply for better marketing because the original title did not click with viewers. It could well be that some overpaid executive somewhere thought that Unleashed sounded more like the action movie it is than Danny the dog which could well be mistaken for a family movie about a dog named Danny.

There are also some odd cases such as Jackie Chan's Armour of God and its sequel, Armour of God 2: Operation Condor:

In the United States, Armour of God did not receive a theatrical release. The film's sequel, Armour of God II: Operation Condor (1991), was released under the simplified title Operation Condor. Armour of God was subsequently released direct-to-video by Miramax Films, but the title was somewhat confusingly changed to Operation Condor 2: The Armor of the Gods, despite being the first film.

In other words, the sequel was released first and necessitated a name change in the subsequently released original.

Wikipedia has a time-sink here with a list of works with different titles in the United Kingdom and United States.

Primary Reason- This is probably due to the cultural difference among the countries. There are various things in a movies title which should be understood but cultural differences make it hard to grasp for the people of other countries. So they change the title so that people from other countries can get the same message.

It started when US movies started being distributed in UK. They also changed to make things sound like there was more action, or to remove subtle jokes for things far more obvious (e.g., Tight Little Island was changed to Whiskey Galore for the US). Later British distributors followed the same rule. This was followed by other countries as well. I don't have, for the time being, any references for the movies you mentioned, but I guess the reason is the same.

E.g., UHF (US title) is "The Vidiot From UHF" in other countries. They did that because people in other countries don't know what a UHF station is. As you can see, they still had that problem with this other title.

Another beautiful example is "Live Free or Die Hard" which was called "Die Hard 4.0" in other countries. Obviously this is a play on the state of New Hampshire's motto, but in another country it would not have any real meaning.

Secondary reason- Sometimes some titles work as a working title for a movie.

Examples:

• Along Came Polly (2004) aka "Untitled John Hamburg Project" - USA (working title)
• Hallelujah I'm a Bum (1933) aka "New York" - USA (working title)

If you're not referring to different release names, then the different names are actually working titles for the movies.

Movies, usually have working titles, sometimes for secrecy (to contain leaks about the actual project), sometimes for the simple reason that a release name has not been decided.

Quoting Wiki on this:

Working titles are used primarily for two reasons-the first being that an official title has not yet been decided upon and the working title is being used as a filler for naming purposes, the second being a ruse to intentionally disguise the production of a project. Examples of the former include the film Die Hard with a Vengeance, which was produced under the title Die Hard: New York and the James Bond films, which are commonly produced under titles such as Bond 22 until an official title is decided upon.

Christopher Nolan started shooting Inception under the name of Oliver's Arrow in 2009. Similarly, another high profile movie, which started shooting under a different name was Aliens - it was shot for months as Star Beast

As a filmmaker, I can tell you ... distribution contracts often contain a clause that states the distribution company can change the name. They change the name when an exec at the distribution company believes they can sell the movie better under a different title. It happens to indie films all the time.