When one looks at the spirituality of the Winnili/Langobards in a historical sense, it's obvious that they ultimately traveled the full distance from Paganism (Wotanism) to Christianity (Catholicism). However, there were many grey areas in between.
Looking quickly through those fazes, we can probably guess that the Winnili very likely practiced some form of Wotanism. During their stay along the borderland with the Gauls, it's possible that there could have been some Cernic (Cernunnos worship) influence, as there was some crossover between Gaulic spirituality and Teutonic spirituality. By the time the Langobards had become Roman allies along the Danube River, they were possibly roughly half Wotanist and half Arian Christian. Arian Christianity was apparently a crude form of Christianity.
In the Langbard Kingdom, Queen Theodelinda officially turned the Langobards into a Catholic nation sometime during the 590s it appears. The native Romanized Gaulic population had already been Romanized and Catholicized for a long period of time. This appears to have been the first step to actually faze out Wotanism altogether. The Langobard nation, although linking themselves with the early Catholic Church, always seemed to have had a hot-and-cold relationship with the Papal institution. There were times where they seemed to float into the Eastern Orthodox camp.
Just a side note, but it's interesting that the Catholics always portrayed Queen Theodelinda as being "less than attractive," seemingly to de-sexualize her, when in reality, it was widely noted that the Queen was very beautiful. Early pictures of her, especially in the Monza Cathedral, portray her in this manner as well. For better or worse, Queen Theodelinda was the St. Patrick of Cisalpine Gaul/Langbard/northern nations, or whatever name one wants to give the land of our ancestors. From every account, and considering that this was a time of political and religious upheaval, she was a great Langobard leader. Strong, widely loved, a woman to remember. She did what she had to do.
Some of the laws of the Langobards give clues as to where they stood on the religious issue after the establishment of the Langbard Kingdom.
From the Wikipedia page Witch trials in Early Modern Europe and North America, under "Protests" (to witch trials and torture):
"There have been contemporary protesters against witch trials and against use of torture in the examination of those suspected or accused of witchcraft.
"643: The Edictum Rothari, the law code for Lombardy in Italy (‘Let nobody presume to kill a foreign serving maid or female slave as a witch, for it is not possible, nor ought to be believed by Christian minds')"
Obviously, at least under the rule of King Rothari, there was still some sympathy for the pagans. This seemed to vary from one ruler to the next, but ultimately going in the direction of Christianity. Although, the end came when they turned against the Church at a time of great inner turmoil in Langbard, and the Kingdom itself was destroyed by Charlemagne's Catholic Frankish army. Ironically the Langobards had long been strong allies with the Franks, and they shared a similar history, conquering and establishing Kingdoms on the lands of formerly Gallic nations.
From the Wikipedia page Val Camonica witch trials, under "Background" (regarding the Valle Camonica region):
"Christianity is not considered to have been strong in the area, though it was formally christened in the 400s. In 724, King Liutprando of Lombardy feared a rebellion after he had issued a ban against Paganism. In the laws of 1498, stern laws are issued against all "Devilish heresy". In 1499, it was accused of having participated in a "Black mass", and it was reported to be common with such "depravity" in the area."
From the book 'The Lombard Laws' (Fischer Drew; 1973), section III 'The Laws of King Liutprand', "From The Fifteenth Year (A.D. 727)," pages 180-181:
"[Concerning him who seeks the advice of a sorcerer]
"84.I. He who, unmindful of the wrath of God, goes to sorcerers or witches for the purpose of receiving divinations or answers of any kind whatsoever from them, shall pay to the royal fisc as composition half of the price at which he would have been valued if someone had killed him, and in addition, shall do penance according to the established canon. In like manner, he who, like a rustic, prays to a tree as sacred, or adores springs, or who makes any sacrilegious incantation, shall also pay as composition a half of his price to the royal fisc. And he who knows of sorcerers or witches and does not reveal them, or conceals those who go to them and does not reveal it, shall be subjected to the above punishment. Moreover, he who sends his man or woman slave to such sorcerers or witches for the purpose of seeking responses from them, and it is proved, shall pay composition as abovementioned. If indeed the man or woman slave goes to the soothsayer or witch without the consent of is or her lord and so without his authority, likewise for the purpose of seeking responses, then his or her lord ought to sell him or her outside the province. And if his or her lord neglects to do this, he (the lord) shall be subjected to the punishment noted above."
Needless to say, this is a sharp contrast from the earlier attitudes towards paganism. Actually, most of the Lombard Laws were very fair and humane, usually requiring simple fines of varying degrees, depending on the nature of the crime. However here, the fine for breaking a law that could stem from simply praying to a tree, resulted in a fine of half that person's total wealth! Further oppressive was the move to outlaw the act of merely not reporting "acts of paganism" to the authorities.
Therefore, the Langobards went from allowing a large amount of personal freedom, albeit in a caste system, to moving to a system in which victimless crimes in this one area was punishable by rather extreme means. Practically "thought crimes." The very next law of Liutprand was labeled "What is to be done if the judge or other public officials of a place fail to seek out sorcerers or witches." I will not type out this law, which had much text, because I think that the earlier law presented the basic gist of where they were coming from. However, here we see that the law officials were not nearly as powerful as the religious institution. Only the king held power over the major Catholic regional theocrats, the representatives of the Papacy itself.
8-4-10 Addition: From the book 'The Lombard Laws' (Drew; 1973), page 247; footnote 55, we find another interesting clue to this subject. It states: "A belief in witchcraft must, at one time, have been widespread among the Lombards or among the naive population of the Italian peninsula. The Lombard kings approached the subject in an enlightened manner, practically denying the existence of this occult science and providing protection against random accusations of witchcraft or sorcery which might bring death or outlawry to the person accused. Such would seem to be the intent of the present law. On the other hand, there are laws in the code (Liutprand 84, 85) which specifically state that it is the duty of royal officials to seek out sorcerers and such like and apply the penalty of the law--sale outside of the country (Liutprand 85)."