The Church does not have a definitive teaching on whether the fires of hell are metaphorical or literal. The Catholic Encyclopedia article you cite prefers the idea of a literal fire but is careful to note (emphasis added):
However, we must not forget two things: from Catharinus (d. 1553) to our times there have never been wanting theologians who interpret the Scriptural term fire metaphorically, as denoting an incorporeal fire; and secondly, thus far **the Church has not censured their opinion. **
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