Also, why does the word for "year" change from god to leto within the paragraph? I know that Russian, for instance, uses both, but surely this is needlessly complicated in an artificial language, isn't it?
Good question!
At least two answers:
(1) if the artificial language is intended to reflect the Natural Slavic Languages, then there are three different words for "year" - roughly, "god" "leto" and "rok" - all of which derive from some proto-slavic word.
(2) if the artificial language is intended to be a simplified language - but based upon what is used among the Natural Slavic Languages - the question then is: Which of the three words ("god" "leto" and "rok") should be used as the "official" word for "year"?
In answering #(2), it becomes a bit more complicated, because, for example, "god" also is the root word in several slavic languages for "hour"
"Leto" also means "summer" in (I believe) all of the NSL's.
"Rok" is used in some NSL, but not in others.
Finally, to make this even more complicated, all of the NSL's used different word forms when counting years, because they did not look at numbers as individual counting items, but, rather "bunched" the numbers into three basic "groups":
First Group: = the number 1 (one)
Second Group: = the numbers, 2, 3 & 4
Third Group: = 5, 6, 7 + ....
So, in Russian we have:
one summer = одно лето = odno
leto
two summers = Два лета = dva
leta
three summers = три лета = tri
leta
four summers = четыре лета = četyre
leta
five summers = пять лето = pjať
leto
ten summers = десять лето = desať
leto
one year = один год = odin
god
two years = два года = dva
goda
three years = три года = tri
goda
four years = четыре года = četyre
goda
five years = пять лет = pjať
let
six years = шесть лет = šesť
let
seven years = семь лет = semj
let
ten years = десять лет = desať
let
100 years = 100 лет = 100
let
one hour = один час = odin
čas
two hours = два часа = dva
časa
Polish, on the other hand, has this:
one summer = jedno
lato
two summers = dwa
lata
three summers = Trzy
lata
four summers = cztery
lata
five summers = pięć
lata
ten summers = dziesięć
lata
one year = jeden
rok
two years = dwa
lata
three years = trzy
lata
four years = cztery
lata
five years = pięć
lat
six years = sześć
lat
seven years = siedem
lat
ten years = dziesięć
lat
100 years = 100
lat
one hour = jeden
godzina
two hours = dwa
godziny
And then we have Czech:
(without coloured font emphasis)
one summer = jeden léto
two summers = dvě léta
three summers = tři léta
four summers = čtyři léta
five summers = pět lét
ten summers =
one year = jeden rok
two years = dva roky
three years = tři roky
four years = čtyři roky
five years = pět roků
six years = šest roků
seven years = sedm roků
ten years = deset roků
100 years = 100 roků
one hour = jedna hodina*
two hours = dvě hodiny*
*("g" in czech and slovak became "h" several hundred years ago)
And this confusion continues on for each of the other Slavic languages - because over the thousands of years that each "tribe" had been separated from the "Mother/Father Tribe" on the other side of the mountains, each tribe developed its own unique form of using numbers and words for "summer" "hour" "year".
So - which form should be used as the common form? 
