This is a bug, as reported on the official Minecraft Bug Tracker.
It was reported as fixed in 14w02a (9/1/14) but reopened yesterdat (8/2/14), so no new date for fixing has been given. However, given that the bug was fixed once before, it is highly likely it will be fixed again soon.
One of you said that the max career level is 4, so I used this command
/summon Villager ~ ~1 ~ {Profession:0,Career:2,CareerLevel:4,Offers:{Recipes:[{rewardExp:0b,maxUses:2147483647,uses:0,buy:{id:double_plant,Count:8,tag:{display:{Name:"Coin"}}},sell:{id:wooden_sword,Count:1,tag:{Unbreakable:1,display:{Name:"Sturdy Stick"}}}},{rewardExp:0b,maxUses:2147483647,uses:0,buy:{id:double_plant,Count:12,tag:{display:{Name:"Coin"}}},sell:{id:golden_sword,Count:1,tag:{AttributeModifiers:[{AttributeName:"generic.movementSpeed",Name:"generic.movementSpeed",Amount:-.10,Operation:1,UUIDLeast:112181,UUIDMost:524106}],Unbreakable:1,ench:[{id:16,lvl:1}]}}},{rewardExp:0b,maxUses:2147483647,uses:0,buy:{id:double_plant,Count:2,tag:{display:{Name:"Coin"}}},sell:{id:leather,Count:1}}]},Attributes:[{Name:generic.movementSpeed,Base:0}],PersistenceRequired:1,ActiveEffects:[{Id:10,Amplifier:50,Duration:133333333333320,ShowParticles:0b},{Id:21,Amplifier:60,Duration:1333333333333333200}]}
and set the career level at 4, this spawns a villager with a career level of 4 that will trade sunflowers named Coin for certain items. Now I tested this multiple times to make sure I was correct, and I was, setting the career level at 4 will prevent new trades from appearing. I am not sure if this works in 1.9, 1.10 or 1.11 because I still play in 1.8.9.
Best Answer
In 1.14, this sort of data is all contained within the villager's
VillagerDatacompound. It containsprofession, which is a string. It can be any ofminecraft:armorer,minecraft:butcher, etc.type, which is also a string. It can be any ofminecraft:desert,minecraft:jungle, etc.level, which is an integer. This should be pretty self explanatory.So an example command might be
You can find all the valid
professionandtypevalues here on the wiki.