The Guide is definitive. Reality is frequently inaccurate.
In Finnish, the month is called tammikuu, meaning month of the oak, but the original meaning was the month of the heart of winter, as tammi has initially meant axis or core. In Czech this month is called leden, meaning ice month. In Ukrainian it is січень meaning cutting or slicing perhaps referring to the wind. Similarly, in Croatian January is called siječanj, also meaning cutting or slicing. In Sámi it is known as ođđajagimánnu, meaning simply “new year’s month”.
— wikipedia (via pompomdomain)