Wikipedia:Milestone statistics

Milestone	Languages (dates milestones reached, in order of reaching them)
250,000	English (20 April, 2004)
150,000	German (10 October, 2004)
50,000	Japanese (25 May, 2004); French (29 August, 2004)
20,000	Polish (14 January, 2004); Swedish (22 January, 2004); Dutch (7 February, 2004); Spanish (16 March, 2004); Italian (22 July, 2004); Danish (5 August, 2004); Portuguese (18 September, 2004)
10,000	Esperanto (1 December, 2003); Chinese (14 May, 2004); Hebrew (9 September, 2004); Bulgarian (3 October, 2004)
5,000	Catalan (14 January, 2004); Romanian (7 April, 2004); Finnish (15 April, 2004); Norwegian (29 May, 2004); Ukrainian (18 June, 2004); Slovenian (14 July, 2004); Estonian (15 July, 2004); Russian (6 August, 2004); Serbian (14 September, 2004)
1,000	Interlingua (31 July, 2003); Czech (27 October, 2003); Latin (7 December, 2003); Afrikaans (9 January, 2004); Walloon (23 January, 2004); Malay (8 February, 2004); Croatian (9 February 2004); Basque (5 March, 2004); Galician (12 March, 2004); Korean (14 March, 2004); Indonesian (March 16, 2004); Simple English (7 April, 2004); Welsh (9 April, 2004); Greek (24 May, 2004); Frisian (6 June, 2004); Hungarian (7 June, 2004); Turkish (15 July, 2004); Icelandic (26 August, 2004); Arabic (31 August, 2004); Asturian (2 September 2004); Slovak (8 September 2004); Kurdish (13 September 2004); Luxembourgish (17 September 2004); Bosnian (30 September 2004)