Dear Anders,

whilst the principal of accounting is pretty much the same everywhere (let us remember that the prinicpal of the balancesheet has been invented by an Italian Monk almost 500 years ago) local accounting principles accross Europe are quite diverse. The UK GAAP as well as Scandinavia and the Netherlands following in their accounting principals the idea of transparency of financial affairs from a point of reasonability and having said that, the solution the accountant choose must make sense. I guess your aplication grants the user the freedom to decide this himself.
In countries like Spain and Italy, but also Belgium France, Germany to a lesser extent, the accounting principles have a rather legal approach, hence the reporting standards are determined by law. This goes to the exterme, that in countries like Spain you have to deliver at year end your financial statements coded according to a chart of account predefined by the local authorities. (Workaround could be that you provide just what you have and the user can create a remapping table for local reporting offline in EXCEL, but that doesn´t sound very user attractive and requires the SMB user to be accounting skilled which often they are not) Another challenge you may face is, that each leger is required to have a sequential numbering for their records, each legdeger having its own sequence. To be competative you should also have an interface for periodical VAT reporting, never mind other stautory reports required like reports to Central Bank and Intrastat in case the user is in the Import/Export business.
You can overcome the issue of local required charts of Account by creating a table of an alternative CoA, which would allow the user to remapp the rollups of his, (let´s call it commercial CoA) into different reporting position according to local requirements.
Concerning the VAT returns to be filed, please keep in mind, that in Italy and Spain, usually there is no money returned if you have a VAT receivables as result of your periodical VAT computation. Instead, it is a netting procedure, whereby the authority nets your credit with payables to come. Same in Italy. Would be userfriendly if you integrate a similar account tracker for the Spanish/Italian User.
Concerning depreciation schedules for fixed assets and prepayments.... as longest you leave the freedom on the user to determine the time and percentage of depreciation, you should be fine without extra modification work on your apllication, unless you provide the user with some local template setups .
So I guess, since other SMB solution providers ,like Intuit for instance, did overcome this challenge, I would assume you will too. 
We are not certain about software certification in Spain before release to the market

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