Here's the Welsh version:
Un dydd ar y tro, fy Iesu - Yma fy hunan nid wyf ond bychan
Dysg i mi weld yr hyn ydwyf i a'r hyn allaf fod
Dangos fy nghyfle beth bynnag y bo
I weithio dros Dduw, ond dysg i mi fyw - Un dydd ar y tro

Mae ddoe wedi mynd fy Iesu - A fory gall fod yn rhy hwyr
Bydd di wrth y llyw i'm harwain i fyw - Fy nyddiau yn llwyr
A dysg i mi wneud fy ngorau - I bawb bwy bynnag y bo
O Iesu, fab Duw, dysg i mi fyw - Un dydd ar y tro

Buost dy hunan ar ddaear fel fi
O Iesu, fab Duw, dysg i mi fyw yn fwy tebyg i Ti
Cerdded ar y llwybr er garwed y bo
O cymer fy llaw beth bynnag a ddaw
Un dydd ar y tro

One day at a time, my Jesus - Here by myself I am but small
Teach me to see what I can be -Show me my chances whatever they may be
To work for God, but teach me to live - One day at a time

Yesterday has gone, my Jesus - And tomorrow it may be too late
You'll be at the helm to lead me to live - My days completely
And teach me to do my best- For everyone, whoever they are
Oh Jesus, son of God, teach me to live - One day at a time

You yourself were on the earth like me - Oh Jesus, son of God, teach me to live more like you
To walk the path though it is rough - Oh take my hand whatever may come - One day at a time

from http://www.dysgwr.com/content/pdf/ACEN%20%28Hydref%20-%20October%202006%29.pdf

Bendithia, Chris