Introduction
SWF is a proprietary software vector graphics file format produced by the Macromedia Flash software from Adobe Systems (formerly Macromedia). Intended to be small enough for publication on the web, SWF files can contain animations or applets of varying degrees of interactivity and function. SWF is also sometimes used for creating animated display graphics and menus for DVD movies, and television commercials.
The Flash program produces SWF files as a compressed and uneditable final product, whereas it uses the .fla format for its editable working files.
The name is a backronym of sorts, standing for Small Web Format and Shockwave Flash. According to Macromedia, SWF is pronounced "S W F" (with each letter being pronounced individually), but some people prefer to pronounce it as "swiff". A file of this format is called a Shockwave Flash Object.
SWF is currently the dominant format for displaying animated vector graphics on the web, far exceeding the W3C open standard Scalable Vector Graphics, which has met with problems over competing implementations. (Source: Wikipedia)
Handling SWF files in DVX
If you got here, you probably did not get the texts for your Flash animation handed in Word. Instead the client gave you an SWF file, which means that the client wants you to act both as a translator and a web designer. It is important that you realize this.
Also important to realize is that SWF files are actually derived from FLA files. Therefore you should always try to work from the original FLA format instead. There are two exceptions, which are SWF files which have been specifically prepared for localization (see 'When to localize from SWF' below) and SWF files that are used to feed DVX with the source text (see 'When to decompile SWF back to FLA' below).
When to localize from SWF
Several websites, amongst which the famous tt4t.net, recommend Avral's Tramigo for localizing SWF files. However, this only works if the SWF files actually contain translatable text, which is often not the case.
The problem is that Macromedia Flash, the software in which SWF files are made, allows the user to convert text to non-dynamic (non-editable) formats. As soon as this is done, the actual text itself is not accessible anymore in the generated SWF file - you can then only access it from the original FLA file from which the SWF file was generated. For this you will need the original FLA file and Macromedia Flash, which comes at a price.
Tramigo can be handy, but only if its usage has been taken into account during the actual development of the SWF files (all translatable text should be dynamic), and not as an afterthought. This means that in the vast majority of the cases, Tramigo won't help you.
When to decompile SWF back to FLA
Sothink's SWF Decompiler gives much better results. It can extract all texts from the file, because it basically converts SWF files back to their original FLA format, with very good results. SWF Decompiler also has an option for exporting text resources. To import them into DVX, you will need to open hundreds of little text files and manually insert hard enters, but that's still quicker than manually copying and pasting everything to a DVX import document. Unfortunately there's no easy way to export your translation back. Text in SWF Decompiler cannot be edited, so you will have to open the decompiled FLA files in Macromedia Flash, which only supports old-fashioned copying and pasting.
For a good localization you will need Macromedia Flash anyway, as you will need to resize some of the text boxes to keep the lay-out nice and tight (think Microsoft PowerPoint). For this, you will also need the actual fonts (the price of which can range from several dozens to several thousands of dollars). Which fonts you need depends on the fonts defined in the SWF file. If the used fonts cannot be traced or are too expensive to buy, consult the client about alternative (cheaper) fonts. You could for example opt for Univers if you can't find Lucida Grande (Wikipedia has great information about font families and look-a-likes). Also, some software packages, like CorelDraw, offer many professional fonts for free.
If you want to start localizing SWF files professionally, you should prepare yourself for an extra investment of about 800 USD (for Sothink's SWF Decompiler + Macromedia Flash, excluding fonts). Be prepared to charge at least 150% of your normal rate, as localizing SWF files is a lot of work, no matter which tools you use.