Simon
New version, updated to work with the latest version of Songbird.

This add-on examines the meta-data of the playing track and searches for lyrics from The Lied and Art Song Texts Page .
The Lied and Art Song Texts Page is an archive of texts used in many, many Lieder and other classical art songs (Kunstlieder, mélodies, canzoni, романсы, canciones, liederen, canções, sånger, laulua, písně, piosenki, etc.) as well as in many choral works and other types of classical vocal pieces. The collection currently indexes texts and translations to English, French, Italian, Dutch, German, Spanish, Portuguese, and other languages. The site has frequent updates.
Display
This Songbird add-on searches for and displays the lyrics for the playing 'art song'. It identifies, displays and stores composer, lyricist, opus, catalog number and song cycle data. When displaying lyrics, it also displays additional data from the Lied and Art Song Texts Page: dates, poem names etc.
Local and/or web art (from lastFM and Freebase) is displayed for composer and lyricist (you can scroll through multiple images with the mouse wheel.)
Meta-data processing.
In order to search Lieder Lyrics by song name, the track title and album name are examined to identify and remove the opus number, catalog number and composer and lyricist. If necessary, these are stored in (new) properties of the media item.
Opus numbers (including 'ohne opus' and 'opus posth.') are recognised by their form; catalog numbers are identified based on a Freebase database of music catalogs. If a composer you need isn't there - please add them!
Composers and lyricist are identified by comparison with the names on the other tracks in your main Songbird music library.
If a composer is identified the Lied and Art Song Texts site is searched for that composer. If no single composer can be identified, or the song is not found on that composer's page, the site is searched by song name.
When a Lied and Art Song Texts Page is found all available data about the track (song cycle, opus/catalog/sequence number etc.) is used to try to identify the appropriate setting.
Lyrics Display
When a setting is found, any missing data is stored and displayed as well as any additional data: year of composition/publication, poem group etc. Missing/incorrect accents and capitals on the track are corrected. (Lied and Art Song Text Page data is always taken as correct. If you find what you think is an error, please check it and and if you are sure, let Emily know.)
A link to the lyrics page is stored on the track; the lyrics (and notes) are fetched and displayed and will always be fetched and displayed whenever the track is played. (A 'clear lyrics' (scissors) icon clears the link from the track.)
If a single setting cannot be identified for a song, the number of settings is displayed ('?' if 10 or more) by the composer name or song name. Click on it to see a list of the settings from which you can choose the correct one.
If a song is not found, check the spelling on the track name. If the spelling is OK then the song probably isn't on the Lied and Art Song Texts Page but please check- if it is there let me know; if it's not there submit it!).
Lieder Lyrics will display any plain text and HTML(?) stored as a track's lyrics (either fetched by another add-on such, Lyrics Master or cut-and-pasted, including with Text Store).
If no lyrics are found they will not be searched for again automatically until at least 23 days later! You can start a search for any playing item, at any time, by clicking the search (magnifying glass) icon.
Please note:
I am sharing this add-on (which I started for my own use) with the kind permission of owner of The Lied and Art Song Texts Page. Her site is well worth a visit; it's a fantastic asset for music lovers and a ongoing tribute to her exceptional commitment to the art form.
You can email me at songbird.liederLyrics@gmail.com with any queries, comments or bugs.
As at 16/12/2011 the email account is now working!
Update to work with versions up to Songbird version 1.11
Simon
1st version posted.
This add-on will always be very sensitive to spellings, formats etc.
It works surprisingly well for me- mostly English songs and German Lieder- but it is not practical for me to test all cases/languages.
Please, let me know, here, when it fails (song name and lyrics page ref).