The terminology of musical notation presents a particular L10n challenge as musical notation is essential a language of it's own that has co-evolved with it's host language. 

Literal translations of quarter note, eight note, etc. by localizers not familiar with the language of musical notation will almost certainly be incorrect, 

By way of example, the following groupings of WP links represent the same concepts in English, Spanish and French, respectively.

http://en.wikipedia.org/wiki/Eighth_note
http://es.wikipedia.org/wiki/Corchea
http://fr.wikipedia.org/wiki/Croche_%28musique%29


http://en.wikipedia.org/wiki/Quarter_note
http://es.wikipedia.org/wiki/Negra
http://fr.wikipedia.org/wiki/Noire_%28musique%29


http://en.wikipedia.org/wiki/Half_note
http://es.wikipedia.org/wiki/Blanca_%28m%C3%BAsica%29
http://fr.wikipedia.org/wiki/Blanche_%28musique%29


http://en.wikipedia.org/wiki/Whole_note
http://es.wikipedia.org/wiki/Redonda_%28figura%29
http://fr.wikipedia.org/wiki/Ronde_%28musique%29


Within any of these articles you will find a table pointing out the variations of musical notation against the background of various host languages.


I would strongly suggest:

1) Including the lang-en wiki link as a translator's comment in the code (to appear in the PO file as shown below).

2) Pre-translating (or confirming) as many as can be done by "wiki-lookup" via the interwiki language links in the lefthand sidebar of Wikipedia in order to pre-empt well-meaning, but inaccurate, literal translations of the Engllish musical notation language being mistaken for "normal" English language terms.


#. TRANSLATORS: http://en.wikipedia.org/wiki/Eighth_note
#: ../src/piano_composition-activity/piano_composition.py:238
msgid "Eighth Note"

#. TRANSLATORS: http://en.wikipedia.org/wiki/Quarter_note
#: ../src/piano_composition-activity/piano_composition.py:260
msgid "Quarter Note"

#. TRANSLATORS: http://en.wikipedia.org/wiki/Half_note
#: ../src/piano_composition-activity/piano_composition.py:272
msgid "Half Note"

#. TRANSLATORS: http://en.wikipedia.org/wiki/Whole_note
#: ../src/piano_composition-activity/piano_composition.py:284
msgid "Whole Note"