Actually, you can localize the reports generated and the web interface quite easily:
The translation file is located in your repository (e.g C:\ProgramData\Seal Report Repository) under \Settings\Translations.csv and can be edited with Excel.

Just add a column corresponding to your language:
The first line contains the language name(= Two Letter ISO Language Name).
Then you have one line for each reference text to translate.
Then just save the translations file keeping the CSV format.

You can then specify the langage used by the product using the Server Manager application, the click on the menu Configuration->Server Configuration...
and specify the default culture of the product.

You can overwrite this culture value per report View.

If you are happy with your translations, do not hesitate to contribute to the Seal Report project to integrate them in the futur releases...

The version 1.7 comes also with the possibility to translate the element labels and titles in your reports (call repository translations).

The goal is to define all these private translations in a file is named 'RepositoryTranslations.csv' located in the Repository Sub-Folder 'Settings'.

Run the Server Manager, open your Data Source, and go to the menu Tools->Export Data Source translations in CSV
Then the helper will scan your Data Source and create a working Excel/CSV file,
just copy/paste the lines to the 'RepositoryTranslations.csv' and add the translations for your language...

For the Web Report Server, you can also translate folder names and file names in the same way (use the Tools->Export Folders and Reports translations in CSV option)

You can check the Northwind demonstration: All elements, enum values, names and even chart titles are translated for the main Dashboard...in French only of course.