How to translate the famous saying "路漫漫其修远兮，吾将上下而求索" in Li Sao?
The Wiki link you provided had the following reference:


  Stephen Owen (1996). An Anthology of Chinese Literature: Beginnings to 1911 (New York: W.W. Norton): 162–75.


Page 169 of the book contains the following section:




  I bade sun-driver Xi-he, to pause in her pace,
  to stand off from Yan-zi and not to draw night.
  On and on stretched my road, long it was and far,
  I would go high and go low in this search that I made


Here 路曼曼其修远兮，吾将上下而求索 matches up with:


  On and on stretched my road, long it was and far,
  I would go high and go low in this search that I made


That at least makes one published translation, that you can use. According to the Translations into Western languages on the Wikipedia page, this is, also, the most recent translation.



Other translations include:

James Legge's:


  The way was long, and distant far was my goal; I would ascend and descend, pursuing my search.


David Hawkes': 


  Long, long had been my road and far, far was the journey; I would go up and down to seek my heart's desire.


Yang Hsien-yi's:


  The way was long, and wrapped in gloom did seem, As I urged on to seek my vanished dream.


and Monica Eileen Mclellan Zikpi's


  The road long, long, such vast distance —— I will go above and below in pursuit




David Hawkes' translation is also cited in Pleco's PLC dictionary:


  路漫漫其修远兮, 吾将上下而求索。(屈原《离骚》)
  lù mànmàn qí xiū yuǎn xī, wú jiāng shàng-xià ér qiú suǒ.
  Long, long had been my road and far, far was the journey; | I would go up and down to seek my heart’s desire.